Honestly DRK and GNB are the least dungeon friendly out of the 4 tanks. DRK especially suffers when the person is not at maximum gear lvl for the piece of content they are running due to your main mitigation tool being tied directly to health.

WAR being great starting at lvl 56 and beyond and PLD being decent at lvl 58 and beyond, these two tanks alone can make up for any bad healer in a dungeon. One can argue GNB being good at lvl 45, but lets be honest here. GNB doesnt really get good sustain wise until lvl 82 with HoC.

When comparing tanks in dungeons you have to look at how they perform at minimum ilvl with their kit and compare from there