The real problem with PLD
It's quite simple. PLD is supposed to be the best defensive job in the game and it takes the best gear in the game to be better than a blink tank for staying alive. So square needs to give PLD better spells/gear/abilities/traits for mitigating damage. They're so worried about overpowering it that they make it useless.
On another note, PLD could really use it's own provoke so people can double down /war or still hold hate /dnc.
Between those two things, that should fix PLD.