Purpose of Mana For Most Jobs?

[Sjol]

MP used to make perfect sense and was actually a huge gate to survival and fight stamina over time. It's somewhat funny to see people discussing it like it's hard to find uses for or balance it properly, when it used to do just that.

And it could be used that way, but it seems that SE doesn't really want to use mana as a sustain system outside of rezzers. I know other games have used mana as sustain adding interesting choices to healing, e.g., by making big heals mana inefficient. It could definitely have a place, but SE doesn't seem to be using that strategy, especially with so much healing being oGCD.