Oh I comprehend the -enmity +mana regen component, but it's on 180second cooldown.
It gives roughly 1,000 mana and cuts enmity by 50%.

It costs ~500mp when I've got something like ~4500mp total
So roughly looking at ~11 casts maximum there.

My problem isn't that I'm gaining enmity, my problem is the rapid speed in which I gain enmity.
For instance, a BLM can cast 11 spells and still be sat on yellow comfortably.
A WHM will accumulate red within 5.

This isn't a serious problem, but I think it would be nice to have a slightly reduced enmity gain for the DPS WHM dishes out.
I'm absolutely fine as it is, because it just makes you think more and carefully balance your skills, but quality of life!
The mana constrictions alone are the reason it doesn't work to spam 11 holy, being red also is a kick in the teeth.