Strictly based on hate generation, the tank that does damage along with their enmity skills will obtain more hate. Therefore DRKs Unleash may be the strongest atm, but it's limited to MP unlike overpower.

Personally Overpower never let me down yet, it's amazing.

As far as if it's fair for PLD to not do any damage with it's aoe enmity builder: I think it's fair. Unlike DRK or WAR, PLDs flash has a blind trait added to it. It fits in line with what a PLD is supposed to be, which is a defensive tank.
They do need some aoe though, it's stilly at this point.