Lot of misinformation in this thread. As it is now, parry does in fact increase damage dealt, through Low Blow & Reprisal procs for Dark Knight. But they can't make it useful without reworking all three tanks.

The problem is you can only get roughly a 12% increase to parry rate through gear. Which equates to about 2.4% damage mitigation, and less for DRK DPS, so nobody cares about it. For parry to become relevant in it's current form gear would need to offer at least 4x as much(48% rate, 9.6% mitigation) or more. But then you run into the issue of an extremely powerful parry based MT in DRK & how you're going to buff PLD who has a naturally lower parry rate(even without shield), loses parry mitigation to block, & produces less enmity out of tank stance.

It's better they just leave parry where it is or remove it from gear/food.