It's true that a lot of stuff doesn't come through as cleanly in the anime as in the original material, and the anime really only covers the introduction arc, but I think the main problem is that you're looking at it wrong. It's not a fighting-style franchise, it's more of a comedy SoL with action scenes.
The comedy, at least from what I've read, is mostly the same exact "gag" (see:title) and haha remember when this happens in shonen get it get it. Saitama's too dull to pull off much comedy or slice of life aside from overeacting to small things, underreacting to big things, and having bizarre social obstacles placed in his way.
"Bizarre social obstacles" is a big category, but the odd social aspects of the manga generally are comedy by way of allusion to real experiences in the life of the young underemployed Japanese man, which is ONE's situation prior to becoming a hotshot mangaka. A lot of them transfer well to non-Japanese men, which is why it's popular in lots of countries.
Oh. That... would explain a lot, actually. You're saying OPM is basically standard shonen haremshit, only instead of modeling the tedium of highschool it models the asininity of the workplace, and instead of the awesome main character being reluctantly dragged into greatness by fawning legions of fangirls which then slap the shit out of him, the awesome main character is being reluctantly dragged into officialized greatness by oddball coworkers which then think he's the strange one.
I didn't get Naxza's powertrip haremshit thing until now.
That's because its joke characters are its real characters and everyone, including the author, is aware of this. But, as I've mentioned, it feels like he wasn't brave enough to actually make a series with them, so he copped out and slapped a big PARODY label over it.
Dude, OPM is a series. This isn't some Scary Movie 4 one-off. The fact that it plays off of tropes and of things that other series do doesn't invalidate the series in other respects, nor is there some clear distinction between series which do this and series which are serious in their aim.
My impression was that it was subpar unless you were giving it the pass it was looking for by being subpar on purpose. If Saitama is bland and disinterested to let the viewers stand in for him, and the side characters faff around for a bit before Saitama solves all of their problems because power trip, and the series in general does what it does not because it's not brave enough to be something else but because that's how you be the thing it's trying to be, then that would indeed be an entirely different set of problems.