The MP cost/Damage of spells is a complete mess. Why standardise the damage/cast time/recast, then split the MP costs so drastically between elements?

Surely if you are making the damage more equal, the cost should be more equal too. Otherwise whats the point in using thunder V (10%ish more damage than stone V) at the cost of 300 MP (100% higher MP cost than stone V).

I'm not against the more standardised damage/cast time/recast, I'd like the MP costs to follow roughly the same scale though.