MP is in a strange spot. The players who used to run out of MP most easily were the good players who were keeping near 100% uptime and constantly spending it. Medica II spammers rarely ran out of mana because their uptime tends to be 50-60% and their gear tended to be riddled with Piety because they don't care about stats. It doesn't even limit Raises that much in that example. In that regard it simply became a punishment for playing well.

If we wanted MP management to be a thing, it would take a full rework. Perhaps make dps casts free, or even a small mana restorative and make heals cost mana, including some oGCD's. Balance it so it didn't regenerate fast and it would essentially limit how much healing you have per encounter, encouraging planning and smart use of cheaper heals and discouraging blindly spamming GCD heals.
But it would mean bad players can potentially go OOM or bad tanks drain a healer too much and cause wipes, which would go against their policy of everything below Savage being clearable regardless of player skill.

As for the current state of healers, until we get that rework (if we ever do), what gets to me more is why is Piety still a thing? Seriously. It's frustrating when a 580 piece is worse than a 600ilv piece because of this nonsense stat. Get rid of it, or buff it with added damage so it becomes our bread and butter stat. I'm baffled how it survived an entire new expansion unchanged though.