DRK should get a big heal of some sort. Clemency(1200 pot), Equil(1200 Pot), Aurora(1200 pot over 18 seconds) are all great heals on the others. Abyssal requires 6 mobs to get to 1200 pot but can get more in big wall to wall pulls. It was better when it costed MP since it could actually be worth using multiple times in succession. Anything less and it's automatically worse.

And the other aforementioned 3 can still get their full heal in any fight. DRK cannot. DRK requires AoE fights. With at least 6 targets.