I don't really see it. if we go by Normal Omega all tank busters are magic based. That gives DRK Rampart, Shadow Wall and Dark Mind. On top of that you have TBN for every tank buster. You can't beat WAR with all it's CDs but you are better than PLD.
PLD only has Rampart and Sentinel + Sheltron.
In physical fights DRK and PLD are almost equal when it comes to mitigation. The difference is that Sentinel is stronger than Shadow Wall.

imo DRK only needs a buff as OT but so does WAR. Both fit the MT spot more than PLD does. Though PLD is really ahead as OT afaik.
I'd really like to see some real numbers when PLD actually has to use it's utility kit. Using Clemency yields no damage. So does PoA unless you use it when there is some long casting time and you can't target the mob anyway.