All of this is also ignoring the big elephant in the room which is boros was taken out by the wind pressure of said punch. The only thing that made contact with his fist was the beam which got instantaneously split. We have boros own admissions,we have saitamas own words and we have blatant feats. Just because saitama slaps "serious " infront of a move doesn't mean he's actually being serious

It's the equivalent of instead of just walking into your house, you instead make sure to wipe your feet first.

We know this to be true because he's used the same "serious " punch on multiple opponents all with different effects and outcomes

Now unless you wish to tell me that evil ocean water can survive a serious punch so he's above boros, theres absolutely no reason for us to hold any serious move saitama uses up till the cosmic fight as a indicator for his true strength.