I think coming at from the direction of setting the CD as the first step in the ability design process, is to come at it from a more difficult perspective, that won't necessarily produce a "finished" product any faster or with less effort.
The best bet is....
1) defining what abilties need to be there - the utilitiy tools (interrupts, stuns, cc, knockback, anything not a dps or heal)
2) creating passive abilities that provide a concept to the class
3) creating active abilties that fit the concept of the class design <--- mostly just about animation design & range
4) set the costs of the active abilities based on their base effect relative to baseline abilities in the game.
5) adjust the cost/ CD/ channel time/ effect ~ to achieve something that may be balanced. (I ordered them according their "resolution" of adjustment, cost/ rough<--> effect/ fine)
6) play test
7) cross fingers, launch, and be ready to make adjustments based on how the class effects player experience
* always ask yourself, does this break the game?
I think you may be looking for a corelation there that isn't actually used in developement. Not that a formula for calculating these values couldn't be created. I just think you'd find that such a formula wouldn't actually describe the "balance" between the classes. The reason why I say this, is that while casting time is mostly just a variable that is being used to set the "feel" of play for a particular ability, by influencing player mobility. CD I think has been set mostly for balance in an after the fact fashion. I'm saying HT doesn't heal for more because it has a CD- it has a CD because it heals for more. You could set the effect OR the CD first, and either (or both) could be altered to adjust balance. It's not really the length of the CD that matters - but how many of those casts can you cram into the interval of the longest CD in the game. Classes are not balanced on a cast by cast basis, you have to involve a longer time interval than that. Disturbance illustrates what I'm talking about, because it's a cast that can be shorter than a GCD, just to make it immobile, but it has no CD.
There are a lot of 60 second CDs. So HT isn't an ability that can be cast every 6 seconds ~ it's an ability that can be cast 10 times in 60 seconds. Vs. Deliverance that can be cast 24 times in the same interval. The 2 piece PvE set bonus makes HT a 13.333/sec ability ~ a 30% improvement. HT can deliver healing before being interrupted, at the cost of resource efficiency if it is interrupted. Deliverance on the other hand, doesn't use resource if it is interrupted. The resource efficiency of HT is dependent on the cast being completed in it's entirety. HT also doesn't benefit from force potency in the same way. The relative importance of those unquantified differences depends entirely on play style ~ it's purely subjective. IMHO, the average efficiency of (HT & interrupted HT casts) vs (Deliverance & interrupted Deliverance casts) is nearly the same. Healing without using HT at all, is more than doable, it's just very "bursty", and with Force Potency, Deliverance may actually be more resource efficient. I find myself doing this all the time, simply to conserve casting time when my force bar is full and I'm taking an agressive position on the field ~ and switching to HT and a more safer position on the field when I need to conserve resource. The choice being made based on how likely I am to be interrupted based on where I've chosen to position my toon. That's just how I play. But other players are going to default to always casting HT on CD, may not use force potency for healing, and probably don't even concern themselves with the small difference in casting time. I wouldn't say that they are playing the abilities wrong, or that I'm playing them right, I'd just say that we're both playing how we like to play.
As far as balance is concerned, it's pretty easy to compare the abilities of the ranged classes to each other and see that they were developed from the same starting place. Consular/ Trooper/ Inquisitor/ Bounty Hunter all started from the same template, and that was derived from the same template as all the classes. That template is just the design limitations of the engine. (going to drop the mirror classes now, as the animations are the biggest difference) High Impact Bolt/ Project are essentially the same ability. The same could be said of TK Throw and Full Auto. There are a whole pasel of abilities that are functionally identical between all of the classes, that were added to provide minimal utility functions. The differences in these exist just specifically to differentiate the classes. Trooper was originally denied a ranged interrupt & given a AoE stealth detection ability, for example. Just as sort of a way to create a "selling point" for the class. Later on, players demonstrated that the lack of a ranged interrupt was major nerf to a ranged class, and the stealth detect was pretty ~ meh ~ when any AoE serves the same purpose, stealth isn't often used by MOBS in PvE, and troopers have a wide array of AoE abilities.
Some abilties were added simply as fluff to fill in GCDs between cds. Those are the abilities that are the less efficient abilities in terms of cost/ GCDs/ and the amount of damage done, such as Mind Crush & Charged Bolts. Being a DoT, or having the damage applied at the front of the cast, just makes two abilities feel different ~ eventhough they have a similar overall effect. CDs of abilities, and being set up as DoTs serve only to limit the frequency of use. Weaken Mind is a great example, the CD is lower than it's duration, so it's lack of a CD is actually meaningless. In order for it to be used efficiently, it functionally has a 15 second "CD". The closest Trooper analog is probably Sticky Grenade, which also has a 15 second CD. Both are also instant, and thus mobile casts, though Sticky Grenade involves a short stun that works in PvE to mitigate incoming damage. While Weaken Mind does a higher amount of raw damage, shortening the period of time over which the mob inflicts damage, thus mitigating damage. The numbers look quite different, but the two abilities have almost the same effect on the solo game experience, in practice. Having a variety of these abilities gives players the option of playing to their own whim, and making choices in how they flesh out their roations betwen their bread and butter abilities that are on CD or cast on proc. Force Armor is another instant with a messed up CD- because the 20 second lockout debuff it applies ~ it's useful 6 times over the 120 second CD of Reactive Shield, but given the differences in passive damage mitigation between the classes, they're almost the same ability if used on CD during a 120 second battle.
As for AoEs, Commando was given a pile of these with long CDs vs the single AoE of the base Sage build. The devs opted to let dps players decide if they were interested in using more or less AoE, through spec choices. While AoE feels like it works different than other abilities. Its is just a sum amount of dps spread across multiple targets. Those multiple targets could be killed with single target casts in a slightly longer time frame, but that is why AoE is typically less energy efficient dps - because it's more casting time efficient, and it's also mitigating damage. AoE suffers from the limitation that it's output is situationally dependent. If used on a single target, it becomes horribly inefficient. While some AoE has a maximum number of targets defined, simply to prevent the ability from becoming too efficient to balance. Any AoE that is very easy to use efficiently from a resource standpoint, is coupled with a long CD. And short CD AoE comes at the cost of resource or casting time efficiency.
Just staying in the vein of Commando vs Sage as ranged dps classes, you can see how the damage of Commando single target abilities was adjusted downward to compensate for the large amount of "easy" AoE, and the passive effect of armor on damage mitigation. The middle dps trees of both ACs give players access to abilities that compensate for the shortcomings of the base AC & give the 2 classes similar capacities at endgame. Gunnery grants single target abilties while Telekinetics grants AoE. Both specs use on proc casts to boost dps. Both single target and AoE roations end up having a very similar feel. And both specs are considered flat out boring by many players, for exactly the same reason ~ the rotations are boring, and feel almost identical.
I think really all you need to consider if you want to "value" abilities for the sake of comparing them between classes, or designing new abilities, is whether or not the ability CAN BE balanced and whether or not players will enjoy the game play of the balanced ability. Base damage values (before stats are applied), CD, casting time, debuff/buff length, damage type, proc relationship, passive ability modifiers, can all be adjusted to "balance" the ability & give it a unique feel. And on the engine side of, at least this game, I really think all the abilities work exactly the same. They apply a buff/ debuff with a duration and effect, invoke certain graphics files/ animation sequences, and that's about it. Abilities that have all their damage applied at the front, simply have a very short duration defined, and don't invoke a debuff icon. Class abilities & tech tree abilities have no expiration timer for their buffs, but don't invoke buff icons or animations. Speeders inovke a buff and an animation, without a visible duration. Although I imagine that the duration for all passive abilities is actually 9999.9 seconds, and the timers are being reset during loading screens. I suppose it could be tested, by sitting somewhere for 2 hrs 47 min ~ without loading a new zone by logging out, using a door, elevator, or taxi (this would explain the loading screen we sometimes get after riding a taxi). And since there is a cap on the total number of abilities that a toon can learn ~ players who have hit the cap with pets and speeders may be able to learn 41 more if they reset their spec. (passive class abilities have already been shown to contribute to the total number of abilities per toon ~ different classes hit the speeder/pet cap at different numbers - considering that all toons have a maximum of 41 skill points. RotHC will make it obvious if tech tree abilities coount toward the total.)
If you ever gave any class any ability that is high output/ low cost/ with too short a CD - you've made a one or two button class. ~~ Mario~~ Ironically enough, Every class has abilities that either actively, or on proc, let the player feel that jolt in capacity every so often. Force Potency serves the same purpose for a TK sage as Tech Override does for a Gunnery Commando. Both generate bonus dps, one by creating 2 crits, the other by creating time for another cast. Clicky relics and adrenals, do the same thing.
Total output per 60 seconds of casts/ (casting time + (cost - passive regen during the cast)) = rotation value
1) For this comparison to mean anything, you have to convert the resource of each class to a common denomination.
2) Any abilities that require a proc to be used, or consume a proc during their cast ~ cannot be directly "valued" as a stand alone ability. The relative value must be inferred by subtracting the values of the other abilities that enable them to be used, after calculating the value of the whole "string" and adjusting the derived value by the ratio of it's frequency.
3) The 1.5 GCD is used for the casting time of an instant.
4) The regen rate used, has to assume that the ability is being used while regen is at the baseline value. As soon as you throw in variable regen modifiers like the concentration proc, regen dubuffs, emergency regen abilities, or being at a low regen level for trooper/ scoundrel ~ these values just go all kinds of wonky. You end up with sepperate values for every ability used with different stacks of buff on self, debuff on target, etc. The base regen value used for the knight has to estimated based on how much focus is generated in an average 60 second period of mixed ability usage.
5) You almost have to assume that DoTs are refreshed at the optimal rate, and not cast on multiple targets on CD.
6) Mitigation effects from abilities have to be quantified somehow, even if it's just the dps that is eliminated by a KB against a melee target. The good news is that you could actually compare the value of a stun to a dps ability or a heal.
In short, either a lot of variables have to be assumed, or an astronomical number of calculations have to be performed. You could build a formula to accomodate all of the variables ~ but it'd be enormous, without accounting for the unquantified properties of the ability that are situationally dependent.....it's a real mess. But I think you would find that most of the "rock star" (abilities from spec choices), actually have pretty low rotation values ~ and that the classes are actually balanced mostly on the filler abilities..... at least in TOR.
If you want to get some broad idea about class balance, the passive mitigation abilities of tanks and armor proficiencies must be somehow estimated as a form of healing. The amount mitigated must be based on the length of the sum casting time multiplied by an average amount of dps. You can't ignore the effects of the passive abilities on class balance.
The biggest variable is always an unknown quantity ~ the player. Environmental variables also play a huge role. Target resistance to specific damage types completely rebalance the worth of many abilities. The sum total, of the incredible number of variables used to define a toon, and in the calculation of the ability effects results in emergent properties. It's just the result of stacking so many layers of variables. Create enough layers of variables/mathematical operation and emergent properties always result. Predicting the behavior of systems with emergent properties, takes a whole lot more computational ponies than it does to build a MMO server farm. You wouldn't get one descrete value for an ability anyway, you'd get a whole series of clouds. And you'd still have to compare how the clouds overlapped with certain variables assumed. I doubt very seriously any MMO class has ever been designed on paper, that made it into a finished product unchanged. That's the whole reason why they have play testing. That's why no one can really predict how changes will be recieved by the players, or what the players will do with those changes in the meta game. And it's why MMO "balance" is always an ongoing process.