Jinrya-Geki you said it.
I think AoE toggles for every spell though, not just thm/blm

All teir elemental spells should have the same dmg base by tier, making water as useful as fire as useful as thunder. Of course using them against weak/resistant mobs would affect this, as would your [element] attributes and [element] attack magic bonuses.

That resistance building thing is a little extreme, I'm not a magey type but what I've seen if your first cast gets partially resisted your simply fk'd, I get why they have it ramping up, it's just a little too much too soon.

Cnj/Whm imo needs to go back to what the majority of the series has had as WHM banish/holy/cure and other Light based stuff.

A final thought, on the number of abilities, magic users have always and should always have more spells than melees have abilities, this makes sense considering that in most instances a mage will only have 2~3 spells that are actually useful in a fight while a melee will be able to use all abilities every fight. But if to keep it simple enough for 6 year olds to play they want to keep the minimum ability count they've got going now, then just drop all the tiers and have spell dmg scale w/ level, you get 1 direct dmg attack spell of each element, 1 DoT spell of each element, and have 3 slots left over for other abilities.
Edit: of course this level of reform would prolly not be feasible at this point in things.