Yep, DRK is really strong defensively with TBN on 15s. You forgot to mention dark mind as well, although that has less usefulness in dungeon trash, it's incredible on bosses, especially someone like innocence who has magic autos.

Offensive AOE is fantastic on DRK, you will output as much damage as DPS on big pulls. That's their next best form of mitigation, kills the packs very quickly.