>>280367440He doesn't have infinite strength though. But he got no limit to his potential. He was struggling against Garou for a bit, then he "zenkai boosted." Garou did the same, and they keep repeating this cycle until Garou hits his limit. But since Saitama has no limit, he already outclassed Garou and already blowing planets left and right, and at that point, Garou already lost.
I think the idea of Saitama power is his growth. He'll get stronger over time based on his opponent strength, and there's no limit to his improvement. At least this is the case with Murata's Saitama.
Logically, to beat him, you'll need someone to absolutely outclass him from the start, and doesn't give him any chance to grow by killing him in one blow. Else Saitama would just scales to his opponent over time, +1 them over them, and won.
DB characters are powerful enough, but there's only a few of them who are smart enough to do it.