What if casters had element resistance debuffs?

[Waliel]

That said, if BLM got a Fire Res down cooldown, I'd expect it to be balanced around their personal DPS, rather than any interaction with RDM/SMN. The benefit is sparse at best, as everyone has already pointed out.

I quite enjoy being the super selfish deeps that doesn't provide for the rest of the party, so how about something that reinforces that idea? An inverse raid buff of sorts. A trait that increases BLM damage by X% for every DoM (except other BLM) job in the party. You'd always have at least two healers so that would be the baseline. Call it Mana Battery and have the tooltip be "Leeching minute amounts of Aetherial energies from other magic users," or something.