Issues with Piety as a caster, specifically a healer

I'm only 27 right now, haven't put as much time into the game as I'd have liked in the past week, but there's something that concerns me.

This is complete speculation on my part, I'm not at end game but it might be worth noticing, considering raid difficulty will continue to increase. I can't figure out how a baseline boost to max MP is supposed be any sort of valuable place to allocate stats when in a 10 minute fight your gas tank is running purely off of regen. More Max MP will give you a few extra casts at the beginning of the fight, and unless there's some sort of 45 second lull in the fight your MP will never regen back high enough to see another benefit off the Max MP gain again.

Piety needs to see some sort of change that is going to benefit a caster over the course of an entire encounter, or I fear nobody is going to take this stat seriously, especially for a primary stat. I can't tell you if the answer is a regen component, I can only tell you what I see right now.