The good news is at least on the operative none of this matters. My main is a sawbones and like you I had all these problems leveling.
* Dissapearing Act or whatever it is called for a operative, it is your "get out of jail free" card for gold fever dps. Don't be afraid to use it and let the dps and tank tank die.
This first thing I did leveling when dps didn't follow kill order, is run into the middle of the fight where the dps is spamming their AoEs. The unattacked mobs are after you because of healing threat, if dps or tank damage them they will attack whoever damages them. Blow your defensive cooldowns and run for the fight. You use a knife to stab people in the back, you are not range, so get into the fight. If you need too throw your flash bang to slow down the mob and buy yourself time. Once the mobs get aggored by others, then worry about keeping group on feet using defensive cooldowns and flash bang when needed.
This gets way easier at level 40 when you get AoE heal, but this will get you use to making it more effective by not being a range healer. I am not saying stand right in the middle of the fight face tanking the boss, in most fights you want to be behind the boss, but I like to be in close proixitey of tank. Especially when you have leaping dps. They leap to a add on the other side of the boss from you and you have all types of problems getting them in range until after level 51 when you get roll.
With a sage I play much the same way, I like being where I can hit all four with the golden puddle, with me standing just at the back edge behind the boss. Again not much of a issue after 51 when you get your 10 sec safe zone that is a aggro dumb to boot. Just do that and watch mobs run off and attack dps/tank from you worry free bubble.
Of course once 55 and geared, either class can just AoE the mobs to death, who needs dps then.
My other advice is always assume dps has no clue what a defensive cooldown or medpac is. Some do, but you never know who will pop one.