Is Saitama really a Gag Character?

I have a question that's been on my mind for a long time now since watching and reading all of OPM. Where did the "Saitama is a gag character" argument come from? The reason I put this here is that I only ever see it in power scaling. People usually say something along the lines of his gag is that he one punches everyone thus he beats Goku or some mid-high teir comic character but this gets disproven by Boro and Garou. The author One even states that OPM is a story about a protagonist at the end of his journey being told from the start. To me, it feels disingenuous to his character to simply write him off as a gag character. I can talk about Saitama's character depth and analysis all day but I'd love to hear your opinions.