... I'm curious what the differentiation is between Support and Damage Dealer, overall.

Like, every DPS besides BLM and SAM has party buffs. Sure I probably wouldn't call MCH a support if you put a gun to my head since it offers nothing the other Phys Ranged lack, but that just makes the question, where IS the line?
SMN has oGCD healing skills while Phoenix is active, as well as its own Raise, but you class it as Damage Dealer here. DRG's buffs are strictly useful for increasing damage output, but you class it as a Support here.
And then RPR, NIN, and MNK are kinda in a nebulous space in the middle depending on your definitions. Would their assignments be arbitrary?
Would Role Actions still be sensible given this extra categorization of jobs?
What would such divisions mean for jobs that have Raises? It seems right now the devs have mercifully given up on the "Raise Tax" since Raises are self-taxing, but if you pit some Supports with it against others without, would they have to be brought back into consideration?

I think this invites more challenges than it necessarily solves.