[Daisuke]

So because they have high skill growth, only a gunner should effectively make use of it is what you're saying because I already know gunners have a good time making use of it. That's only 1 class out of the many other classes.
Even monks have a hard time keeping their FP up to 90-100% because power up only gives 16 FP and costs 6 momentum. The only ability that has less FP than that is meditate. Kensei has it easier because they're only there for the passives.
And yes, BKs have no FP management, that's why I used them as an example. Neither does Ghost, Arbalest, Engi, Verglas, Evoker, and Lantern Bearer. They have 0 way of using this skill aside from walking and normal attacking until they die just so they can get a decent bit of health that's most likely not even half their HP unless they're a mage.

Racials are geared towards certain classes(plural) but they aren't geared towards a specific trait and a specific promo. Lich passive is good for ALL mage classes. Elves are good for ALL healer classes. Umbrals are good for ALL spellcasters. Do you really think Phenex is supposed to be geared to battle spirits and vampiric shell? They also tie in with their lore too and make sense. Last I checked, Lich was a being of arcane energy which explains their FP, Hyattrs had huge lifespan and their patron deity was a massive dragon which explains their Vit, Redtails are known for being extremely lucky, etc. There's nothing implying that Phenex know their way around guns. Instead they have faith growth and they also happen to have really balanced stats which make them suitable for almost any class.

It really seems like you're hugely overestimating the Phenex passive as if it's some forbidden racial that shouldn't be touched.
It's not as good as you're making it out to be and doesn't need this crippling requirement.