Just in case (I'm not saying it's enough), I just wish to add some numbers to the discussion : for warriors, tank stance put their dmg power at 80%, and the dps stance at 105%. Just by looking at those number : 105/80 = 1.3125 --> in tank stance, the tank deal 31.25% more dps than in tank one, without even counting the new skills he has access to (and the more you have dps, the more you generate enmity too, and again I'm not saying it's enough to compensate for a long while).
Now that's said, the warrior's tank stance only make healing effects used on them better of 20%. I am wondering if it really can make a difference for the healer to be from "I could have a lot of dps while tank is in tank stance" to "I can't even land a damage oGCD because the tank is in dps stance".
If a warrior is in dps stance and use defensive CDs, I guess he will be tanky enough for a little while to let healers at least use their best dmg oGCD and maybe some important dmg GCD (but I don't know healers enough to know what deals most of their dmg).
