Yes I’m power scaling, fuck you.
If Viltrumites (from invincible) invaded the OPM universe, how much effort would Saitama have to put in to defeat them? Each and every one of them basically scales the entire universe, so I can’t imagine he’ll be able to one shot all of them, but would they give him the fight he’s looking for?
The strongest in the series is at or just under Boros level. Probably just barely capable of planet busting but never confirmed. He would be able to do it through sheer brute strength instead of needing an energy attack, so physically would be Boros’s superior. Saitama could one shot them all, just a matter if he can do it without sacrifice a hemisphere.