The Prison Ralm experience didn't necessarily make Gojo stronger, it's just that he wouldn't have that quickly managed to pull it off if it weren't for the PR. Knowing Gojo, he'd have done it either way after getting his domain destroyed a couple of more times. It's not like altering the domain's conditions is a huge task for him. While having different experiences is definitely an advantage, you can't outright call it a power-up. If we're going that route, Sukuna's way more experienced than Gojo.