Casting a particular spell will always give you X amount of XP for it, even if you decrease the cost of the MP to use it. So casting Minor Change (Lvl 5) will give you the same amount of XP as Minor Change (Lvl 1), but you'll be able to do it a lot more cheaply, so you can spam it more often.
So for example, change XP distribution to levelling up only individual spells. Level up one spell to only cost 1 MP to cast. Then change distribution to only level up the magic type, and not the spell itself. Now, every time you spam that 1 MP spell, you're levelling up the magic type instead of the spell.
Etna has no idea what PMMM is! I was willing to let MagAd go pure crack and take that form by 'coincidence', but there'll be no creating illusions of Kyuubey in this one!
I'll fight you.