I like this, what if we make a regeneration rework alongside it?
Make grey hp have no regen in combat, only out of combat, then rename regeneration stat to spirit and make it so it regens your grey hp a % of the hp you regen from your green bar, so if you have a 100% (it can go beyond 100%) spirit stat you’d be regenerating 7 green hp and 7 grey hp every second, assuming there’s green hp to regen, which would only be the case if your grey hp was already depleted or if your fighting someone with armor piercing.
Lastly, make the “revitalizing” effect from the vitality rework also only heal grey hp by the % of their spirit stat, so only a vit class would be able to get the most out of the spirit stat, which just makes sense.
I think this would make defense way less meta, since running high defense would be kinda bad unless you run high spirit alongside it, but since both defense and spirit get countered by armor piercing, running high defense and high spirit would only really be viable by a vit class