All classes do something. But only one class is best at one thing. Conj are not "Cure Only" but they are BEST cure. THM are not nuke/debuff only but will have the BEST nukes/debuffs.

My position is based on that. I don't think people are going to trade a best cures for Not-as-good nukes in a party situation, when they can just as easily have a BEST cure and a BEST nuke