Tanks are supposed to worry about their health and their ability to hold aggro on their target(s). this is a long established pair of facts.
Damage dealers are supposed to worry about their outgoing damage, and staying alive and not risking the well-being of the raid. again, these are well known facts.
if tanks do more damage than damage dealing classes, what's the point of damage dealing classes? why don't we just all roll brewmasters and take turns taunting the boss and doing awesome dps?
the point of the nerf vengeance argument is that it undermines damage dealers and makes them feel inferior, when it may or may not have anything to do with the tank's skill level, and may have more to do with standing in fire on purpose to shoot their vengeance up.
when i first hit 90 a day or 2 into the expansion and went prot so we could kill galleon, i was top dps by a large margin. i was shocked, and i quickly thought to myself, "it must not scale well, or else tanks are going to outdps the dps classes, and that would be stupid." lo and behold, months later, here we are, tanks purposefully standing in bad and doing 500k dps.