Actually, you're doing 83% of the damage that Gapezilla is doing there and you both got rank 3s for your class.
Do you think it's fine for a tank to be doing as much damage and healing as you are on live or have been doing on the PTR in testing? Don't get me wrong, it felt great to crush the meter on M Butcher, but it wasn't balanced.
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You're arguing from an imaginary standpoint of where you think things should be and not facing the reality of where things are. Not all DPS are Arcane Mages and they never will be. If anything, Blizzard probably wants to bring them down a bit rather than everybody else up. From your first paragraph and your last, it seems like you just want everybody to be doing the exact same thing. All specs do the same amount of damage in (presumably) every situation. That sounds lame to me.
From a game design standpoint, the reason tanks shouldn't do the same amount of damage as a DPS is because then they would just be upgraded DPS and not a separate role. "You can have two overpowered DPS per raid" is all that raidwide debuff would mean. To clarify, I mean overpowered in the sense that they do the same damage, but have much better survivability. It would feel like shit to be the second string DPSers, and that is an important point. You don't want to marginalize DPS players in that way. Keeping the trinity has worked for them so far and they aren't going to change that. There's no need for them to reinvent the wheel.
Within their design concepts of tanks doing less damage than DPS, they can improve tank gameplay by giving everybody a Harsh Words analog, bringing all tanks into line from a damage perspective, and giving us more specific jobs. I think the third one is incredibly important. If we actually have things to do that are specifically designed for tanks, then we will actually feel more like a different role and less like subpar DPS players.