The removal of Stoneskin (which isn't confirmed yet, btw), is probably because they didn't want to keep having HP% based shields, since they would only get better and better with time.
This is nonsense, as we discovered with Heavensward. HP pools increase, but so do healing potencies. It's not like everyone's health is spiking up by 500% while heals go up 10%. Should we drop Adlo's potency, because with higher mind values it'll just get better and better with time?