[Shujin]

pretty much just ignore diminsihing returns or scale down the HP cost per turn by a lot, cause its almost never worth the HP trade off.

Else instead of flat stats, getting sub stats like direct SWA/HIt/Dodge maybe even DR.

or any mix of the above would make it more useful. That it hurts yourself more than you can ever hope to dish out with it on including momentum costs makes it near unuseable outside of some niche cases where you abuse selfhealing with selfstunning. though thats not really the intended use.