Wow am I late to this one... Just wanna throw some math out there.

DRK: Grit + Darkside = 0.8 * 1.15 = 0.92x
WAR: Defiance + Maim = 0.75 * 1.2 = 0.9x
PLD: Shield Oath = 0.85x

So actually DRK has the most optimal tank dps combination.
They also have higher potencies on their overall combos, and have Scourge to level out Goring Blade somewhat. Maybe not entirely with the Goring buff, but mostly. Much like WAR has higher potency on several of its attacks, Fracture, and better dps CDs.
Basically the only major dps difference between the 3 atm is that WAR has 2 DPS CD's, PLD has 1, and DRK has DA, which can be very situational at times.

That said, A8, first part of the fight, whole lotta magic damage, and a magic mit debuff too!
Sounds kind of familiar doesnt it?