I mean it's functional to BLM/Drk's kit, without MP you'd have to have creative workarounds or another annoying gauge.
It's also good at Limiting Red mage rezzes.
I feel like from a healers perspective yeah it's become less important to healer jobs in general. But I do think MP can have some creative uses if they actually did more with it as a resource management gauge, A example like Clemency being ogcd but costing MP limiting spamming it with the result of damage loss (because you have attacks tied to MP) but also making it more "up to date" with tank kits would be interesting. (Obviously tone down general healing on like magic attacks, tank healing needs to be lowered esp warrior).
Healers could even have strong support actions tied to MP as a OGCD if they wanted to make healers a little more interesting, obviously they would need to warrant that with making fights more focused around healers actually having to consistently heal more often instead of just pressing 1 of your 10 ogcd's.
I'm really not in favour of removing MP as it is, honestly i think it's more of a hassle then it's worth, but it does need a lot of work. I think theirs actual reasons why it's stayed around and I rather they actually do something more with it then remove it, as removing it seems to generally be the SE solution to most things.