I can appreciate the lore reasons, but I don't really like how elemental affinities/weaknesses seem to be implemented for most monsters. It seems like most monsters fall under the generic "Astral" or "Umbral" categories, which means that you really only need to be concerned about two spell groups in practice when determining a monster's weakness (Banish/Fire/Thunder/Aero vs. Scourge/Blizzard/Water/Stone). I guess they could change that without needing to make Astral and Umbral their own separate elements, though, I guess.

From a purely aesthetic standpoint, though, yeah, it feels a little odd to play a FF game with only 6 elements.