I think for MP to be meaningful it has to give you choices and consequences. The most obvious one would be choosing between high benefit, high cost, low sustain versus low-cost, low benefit, high sustain.

That would also require more healing to be GCD or for them to introduce mana costs to oGCD.

I do think for MP to be at all interesting, you either have to have consequences to choices or you have to have it be a limiting gauge like it is for BLM.