"Tanking in tank stance" is kind of the key to having more damage as DRK than WAR as MT - the problem is that rarely will you stay in said tank stance past a few GCDs, and as WAR you only go back in it when Unchained is up... so WAR's MT DPS currently is only slightly behind it's OT DPS unless you have a NIN (in which case you never even need to be in tank stance). WAR's biggest problem as MT is losing IB, whereas PLD keeps Sheltron and DRK keeps DA + DM - if none of these are necessary then you'd want WAR to MT to optimize tank DPS (also lets the PLD or DRK never have to press their enmity combo in their opener which is A+). You can see this in fights like A4S, where it's optimal for the WAR to pull but for the DRK to tank last phase. I think DRK's damage is fine, though, just that WAR edges it out in that regard since it's... supposed to.

I also think DRK's kit is actually pretty well balanced now - the only big problem it has is physical hits that happen in quick succession. This was made obvious by Ravana EX where a DRK would have to split the damage with the group if solo tanking, whereas a WAR/PLD wouldn't. If we see more physical fights with tank busters closer together, then DRK will be in trouble - until then, however, it's CD kit is fine. Even for physical fights, it essentially has the same kit that PLD had and PLD did perfectly fine. I think Dark Dance is a bit awkward as a CD since it's main purpose is to force proc Reprisal... but that really just seems like clunky design. That's my only real issue with DRK atm though, I don't really know what fights we'll have in the future so I can't say for sure that DRK doesn't need adjustments but as it is DRK is fine.