In FF XIV, dps is king. Maybe it should be not, but it is.
I know a WAR than can hold the aggro very easily, but he doesn't make a lot of dmgs. By that I mean even less than the heal. So ok, it's easy for this last one to heal him, but in Trials or Raid, we are risking the enrage just because he can't make a lot of dps.
It's just an exemple, but this is how the game is done: dps dps dps...
Btw, I've read your idea of "DRK is the AOE tank", and it's not a good idea, at all.
So the DRK will be usefull for what? Dungeon? And? That is all.
So the DRK will be useless. And personally, I find the WAR better for dungeon.