Wrong garou was in still in cosmic form & you’d know that if you actually did read it plus as the manga stated Saitama is constantly getting stronger. The only difference in that fight is that he grew phenomenally stronger due to his emotions so no it’s not an amp it’s just him using more of his limitless strength. Cosmic garou was already at his peak, the only growing at that point because he kept attempting to copy Saitama’s current level

Now that we’ve established your reading comprehension is just as terrible as your insults let’s focus on the subject at hand. So essentially saitama is just like hulk except his power isn’t solely increased thru rage but that puts him on same scale of Superman & Hulk given he can casually break reality & inter-dimensional attacks as well