DRK is fine in dungeons that you are not doing trusts with, or bad healers with. DRK is the king of mitigation. It lacks however self sustain to where you have to have more incoming heals than other tanks in dungeon outside of your abysall drain and TBN windows.

Overall the leveling process for all tanks needs to be looked at. Obviously if you do any dungeon on WAR, you can see it is way ahead of its tank counter parts. One will argue this is a dungeon and its casual content, but if one tank is way better in content most people play then there is a serious problem.

We only have to hope there are some serious changes to leveling, self sustain, and mitigation as a whole in the next expansion.