Power isn't simply additive. Each ability has a proper formula which uses the Total power for said attack type which includes Mainstat, Power, Tech/Force Power or Weapon damage (I will oftenly use the terms of Total power with this as a defenition). If an ability has a formula that says that the damage are 2 x Total power, increasing +23 damage in the Total power will give +46 on the said ability. An other ability could have only a 1.3 ratio, increasing its own damge of only +30.
In fact, what should be compared is not how much damage it adds on the statsheet, but how much percentage of Total power you gain from Power. If you're a tank, with low Total power, adding 100 Power *can* imply a percentage bonus higher than the said 2% Expertise gives... I said can because I'm not aware of how much it represents. But the more you already have Total power for exemple as a healer who has much main stat and much power, the less likely putting some Power will help better than expertise. But you also have to take in account the fact that it doesn't increase suvivability like Expertise does, so Power has to give a damn big bonus in order to be better than Expertise.
Your "Total Power" is just the Bonus Damage stat, which encompasses all sources of +damage. Just Power, however, adds an additive increase to the Bonus Damage of 0.23 damage per point of Power, hence +23 Bonus Damage for 100 Power.
I see your point about the Coefficient though, I'm just wondering if Expertise damage modifier gets added on at the very end of the formula and whether it's before or after a Critical Hit? These kind of specifics are a mystery to me, but I still think the Expertise trumps the Power at all currently-attainable stat levels.
Yeah seriously. I have never once, in years of playing MMO's seen a fight that's so intensely close that a .02% increase or decrease in damage or mitigation is the difference between victory and defeat.
You're either going to win or lose by much more than the difference is anyway. Obviously if you have 0 expertise and the other guy has 1500, that's a problem. But if you have 1250 Expertise with more main stat/end and he has 1500 with less mainstats/endurance, you would have to be basically identical in skill (to within a 1% margin) for it to matter.
It's not about the 1% difference in the fight overall, it's about the few percent difference on EVERY ATTACK during the fight. That adds up quickly, just like adding 10 Power to every piece of your equipment adds up to a nice sum at the end, such as going from Battlemaster to War Hero for example. The difference per piece is small, but it adds up. The damage difference per attack is small, but it adds up.