There's no agency in MP management. All the MP you can ever gain is controlled entirely by cooldowns. If you run out of MP, you have absolutely no way of trying to get it back, which means you cannot have ways of spending MP beyond what you generally naturally via consequence of your natural regen, cooldowns, and resources or the player is stuck in a hole with no escape rope. Your only method of influencing MP regen at all is Piety, a stat that is functionally useless. Yes, it gets you MP back, but if the MP generated through Piety was not necessary for you to clear content, as the MP you would've gained without it was enough to give you what you needed, then Piety has done literally nothing. And spoiler alert: You don't need Piety's MP regen 99% of the time, even if you aren't a highly skilled healing master. Because there's nothing to spend MP on. The only time you burn through MP is when the rest of your party is falling apart, which is the only time actually costly resources like Raise or spamming Cure III are ever a consideration.

If your standard spells had no MP cost, but you had a variety of more advanced spells that do, you would have the choice of how to spend you MP and on what. For example, rather than Afflatus Solace and Rapture being free heals available per lily use, why aren't they always available at a higher MP cost? You can heal without losing damage, but rely on it too much and you'll run your MP dry. Meanwhile, you can have a resource that restores your MP on the GCD, but that naturally costs you DPS, counterintuitive to reason you're spending MP on Afflatus heals to begin with. Manage your MP well, and you maintain your DPS output effectively while keeping the party healthy. Fly too close to the sun, and you have a way out, but you'll be undoing the efforts you had worked toward.

I want agency. I want to have ways that I can be greedy with my MP, ways that can result in my success or failure in regards to my DPS output. My ability to keep the party alive and healthy is unaffected, but my ability to do so while maximizing my DPS is affected.