Why is it that ammo is pretty much just a DPS thing? PLD and DRK can use their resource to either DPS or mitigate and have some sort of player governed decision making.

GNB on the other hand is kinda just, you hit the dps button whenever you have ammo. There's isn't any opportunity for cool situations where you save yourself because of smart decision making with your resources, it's just you hit the button and get dps.