If we want MP management while also making sure the new system isn't entirely unfriendly to new players, it should come with the caveat that all basic GCD heals should cost 0 MP, only the OGCD tools and damage kit should cost MP.

With that, you'd have a system where messing up your MP management means you cannot do good damage, but it will never affect your primary objective of keeping the party's HP from hitting 0. New players would also be able to continue spamming GCD heals until they're comfortable enough to learn how to use their other tools.