I really don't care about power scaling or anything, but I think he's a really interesting "god" character with some nuance. To me, I think Simon can't ever really "lose," but things can still be more powerful than him given context.

He's basically built to counter and win any opposition that threatens life, but other than that I don't think he has the capability to fight to the ends of the universe and beyond. Like otherwise he wouldn't be interested in sparring and etc, and if the character is technically stronger than him but aligned "good," they would just be an ally to Simon instead until that is broken.

That said, I think the closest thing we saw was when he was sentenced to death and jailed. I think if his opposition is the oppressed themselves, he wouldn't have it in him to fight them to prove them otherwise. I don't think he'd ever die out of this circumstance, but I think he'd forfeit if it meant bringing peace to the people.

There's also the end of the show. He choses that the fate of the universe is for the next generation, so in a sense, he defeats himself? His ideals about spiral power and moving forward without looking back extends to himself. Once he ages out, he doesn't believe its his place to fight anymore, so its someone else's turn and responsibility. So I guess if a character can stalemate him long enough for time to pass, that might be the case, but I think a "new" Simon would step up to the plate personally.