Is it functioning as 30% of health lost during the battle, or is it 30% of total health like OP claims?Its' only 30% of missing health so if you were knocked to 10 you'd get 30 back, if in the next battle you weren't injured you'd only get 20% back etc.
That said I thought you were arguing against the basic premise of getting lost health back instantly after a battle (which is the mechanic I'd want to keep) so sorry if I miss-understood you. I think we can easily agree on something that would work for both otherwise as I'd be just as happy with being healed to a minimum of 30%, or healing 30% of damaged lost in that battle like warband.
I'm presuming that the bug report is accurate, and that the perk is functioning in a way that 30% of total health is recovered every battle, and that Taleworlds has indicated this is normal and intended. If it's limited to what damage is lost in that specific battle, only, that sounds fine and like what Warband had.