DRK hasn't lost any of its sustain since ShB, if anything DRK is now even tankier with the addition of oblation (even with it being trash in comparison to the other level 82 abilities). The other tanks have just gained way too much sustain in comparison.

If you seriously think DRK is bad and is too much for healers to handle (keep in mind that a lot of healers actually WANT to heal rather than mash aoe while only using ogcds, so it actually works out for them, try looking at the healer forum some time) then you're either out of your mind or really bad at DRK and require the crutch of busted mitigations.

If anything needs to happen to the tanks then it's the healing on PLD, WAR and GNB that needs reducing back to what they were before EW rather than buffing DRK to the point of never needing a healer too.