DRK is completely fine as it is save for a few actions.

Salted earth and Abyssal Drain both have basically no functionality on single target other than pitiful DPS gains... but since every DPS gain is important, it makes it mandatory to use them whenever they are available for no other reason than adding a few digits to your dps. They are a chore.

Would be nice if these had effects that made them more useful as utility than a dps-chore. Increased healing from Abyssal Drain would make it a survival/mitigation tool.

Other than that I think DRK feels great. I dont particularly feel like it is slow like some people do. TBN is powerful enough to make the job feel equally useful to the other classes alone.