Elemental Resistance change.

[SDaemon]

The whole elemental wheel should be brought back, damage and defense as well as the affinities for casters. :/

WHM, BLM, SMN, actually pretty much every class that has access to spells would need to be reworked. Those 3 just come to mind that would need to be drastically and fundamentally reworked to function with an elemental wheel in regards to damage. Bad idea overall.

As far as adding a real purpose to elemental materia for defense, SE would need to add materia sockets to end-game gear other than crafting and buff their bonuses. Not keen at all on that idea. Would also make fights even more gimicky where you need to stack x materia for this fight and y materia for another, leading to having to have multiple sets of identical gear with just the materia melded to them being different. Imagine having to farm/collect 4+ complete sets of Dreadwyrm gear (pre-unlockable spam) and then having to stack a different elemental defense to them in order to get the most benefit when fighting bosses that use different elemental attacks. (obviously BiS isn't fully Dreadwyrm gear so no one would farm a complete set if they want toe benefit the most from their gear, but the general meaning is there)