If, right now a spell costs 2,500MP and we have 25k max MP, after the patch, said spell will probably cost 1000MP.

No matter how you roll the dice, you can still cast it 10 times before you run out of MP. I don't really see the problem here. In fact, I LIKE that the numbers are shrinking. But then if Piety gives MPRegen then maybe the cost is more like 1200 so you can't cast it 10 times straight up but maybe by the time you go to cast the 10th you'll have just enough to do so.

In fact, they already do this in PvP already, have numbers capped at certain amounts and costs adjusted to compensate.