I've cleared UWU and been progging UCOB lately. While DRK has many issues the main three offenders for me are:

1.- Living Dead. Healing it is pure pain if you don't have a WHM in your party, specially at 70.
2.- Dark Missionary. I'd use it more if it wasn't locked at 76. I've been asked to change from DRK to other tank more than once, not having any raidwide mitigation really hurts the party.
3.- Stalwart Soul. I don't know what the devs were thinking when they locked it at 72.

I didn't see anyone complain about it, prolly cuz not enough people run ultimates. I don't ask for much, I'd be happy if Dark Missionary was changed so it unlocked at lvl67 or something like that.