I dont think ignoring the issues of DRK is all to helpful. They are a bit underpowered compared to the other tanks. Case and point, warrior does everything better except magic mitigation: which DRK is slightly ahead on. For PLD, DRK does nothing better than PLD except DPS which they are slightly ahead on, and magic mitigation (everything else they are leagues behind). They are by no means useless, the issue is that the other two tanks are just plain better. DRK has to much randomness, not near enough usefulness as a OT due to reliance on parry, and their mitigation is largely based around parry and self healing, which are two very poor forms of tank mitigation.