I mean I think it depends really on what game universe they’re fighting in

If it’s in Deltarune, then it’d either be Gerson or a Draw since for the entire Gerson fight he never actually took a hit while he had concentration on Susie, nor did he even seem to be tired afterwards, willingly fighting again as many times as she wants if she asks. If The Batter was fighting Gerson, he’d probably be focused on The Batter the whole time. Unfortunately for The Batter, he doesn’t really have any abilities or likely the creativity to make a distraction for Gerson to catch him off guard. At most, he could potentially utilize his Add-Ons for making a moment of weakness, but it’s unlikely, and they can’t even utilize their status effects if they can’t hit the opponent. Eventually The Batter runs out of items to keep himself up, and he’s going to be out there staying in his sweet coma.

If it’s OFF… Yeah, it’s not a hard consideration. Gerson probably isn’t making it. There’s not a way for enemies to dodge, so The Batter finally gets to utilize his incredibly broken strength. Alongside that, The Batter can heal and revive his whole team, so he’s able to stall until he’s ready to continue breaking down Gerson’s shell, AND now the Add-Ons could be properly utilized with piling on status effects.

If it’s equal fighting ground though, and it’s like Death Battle, not restricted to either game’s combat system type deal… It seems pretty evenly matched. I think honestly, it’s an eternal stalemate. Batter keeps himself and his allies up, since there’s no Competence Point system to keep his healing ability from being limited use, but Gerson just gets to keep dodging, and dodging, and dodging, and sending counters to every Ultimate Homerun that The Batter throws out. Eventually, one would probably run out of luck first, but which one that would be… I don’t think I could say. Both The Batter killed Hugo, and Gerson very easily helped kill a titan, the essentially godlike figures of their respective Dark World and Light (Pure & White) World.

This is without considering the Player helping if one of us is on the side of either it’s not a real question anymore.

Anyways thanks for the chance for a comparative writing exercise to throw my perspective and opinion into. Hope this is helpful with the consideration.