Okay so I went and redo the fight. I noticed that, if you do not try to gain strength and maximize intelligence gain at the beginning of the game, then ditch every opportunities to train, you shouldnt have any of your stats heavily modified (other than possibly strength, because you gain free points 3 time before the fight, which at best could give you 1 additional dmg per attack). But even without the 1 more dmg per attack, the best thing to do would be to protect every turn and hope rng will bless you, although it does seem impossible now that you cant literally skip your turn. The best I reached is 4/10 HP. If you really want to get the CG, maybe trying another husbando could change how likely he is going to solo the fight? Since I've only went with Ray and Max so far, perhaps you could try Kody or Alex?
Nevertheless, I wish you best of luck in your quest for the CG
EDIT: I forgot that, to do the surrender glitch, you had to be corrupted-the glitch is still available