A bad DRK or WAR is worse than a bad PLD. PLD just mitigates more by default, the other 2 just have a lot more gimmicks, minibuffs, lifesteal and more complicated rotations, however, bad players won't make use of them. DRKs spamming their aggro combo repeteadly will considerably tank less than say a DRK that uses their souleater rotation and keeps weaving dark arts on it, the difference isn't small, in fact, it's huge. A good DRK can handle pulls of 2 and even 3 mobs with a fairy solo healing it with proper CD management and lifesteal tools. A bad DRK might not even handle 1 mob without a healer going out of cleric and manually pumping heals.