Blocking more means more War Drum and Phalanx spam (required block to use them) and Spirits Within combos with Phalanx, all three of these abilities have enmity boost

Anyway, I don't think PLD threat was ever a problem, the real problem is speed runs and the fact that a Warrior tank makes them... speedier!
Oh and PLD can use some more HP too but that is secondary to the failure of the current dungeon design. Actually, speed runs are OK, but Yoshi-P has stated before that any class can do any content and that's just not true right now.

Well, Dr. Mog had a video of a speed run of some dungeon with one of every class, but we all know how MMO players are, not willing to face adversity when there is an easier path to the loot