Another unpopular opinion:
I just finished this series and I have to say.... while it was an easy read it was so overrated. I heard so many good things and actually really liked the start of the series but man did it disappoint and not live up to the promise so many fans have hyped it up to fulfill. The pacing is fine and probably the second-best part about it, as I said it was an easy read, turn your brain off and turn the pages. There is very little substance to this series, mostly just action and not a whole lot to think about. The characters are almost all completely shallow and lack any sort of depth and the antagonist were mainly introduced just as story devices, so I could not get behind any of them or their goals (did they have goals?). The relationships that Denji was able to form were actually the best part of the series but again the characters are so flat and one dimensional that I could care less about any of them, even Makima who so many fans gush over was bleh (for lack of a better word/phrase). Denji is one of the weakest protagonists I have ever read in anything, and he is so damn cringe that I nearly gave up on the series, except that again it is so action focused that it was easy to read (I read the last 30 chapter in maybe 3 hours). A lot of this series was cringy and I feel like the hype was due to it being a borderline Seinin series in a Shonen magazine and because it was "edgy". Another issue I had is the art was not great and a lot of the side characters ended up looking a lot alike, to the point I had a hard time telling some of them apart. I gave this a 6/10 on MAL and that is probably higher than it should be, but I was able to finish it and not just give up on it so that says something.
TL:DR
Overhyped cringe, if you like action and not having to think this may be your series.
What's your MAL user?
I don't think CSM is edgy, the author doesn't try to make things "dark" or "serious" on the series. He clearly treats gore, violence and other stuff like a B-grade movie, like a trash joke, that's far from edgy. The art is dirty and scribbled in purpose, most of times I just laughed at the action and fighting scenes. I don't even understand why people claim that to be a seinen btw so I agree with you.
If you read any of his other works, you'll clearly that :)
I'm not sure if you're more into series with heavy expository dialogue, in that case I guess Fire Punch(same author) would be more interesting for you. And no, it's not like CSM has a huge depth or sub-text(we're talking about a WSJ series anyway so entertainment is the priority), however in my read I found some interesting concepts about relationships and sexuality. Maybe the fact that you turned your brain off to read it made you not pay attention(and that's alright because I think you can enjoy the manga just for crazy action and insane panneling).
About Denji, I don't like his archetype but as a character he's interesting, at least for me.
I also agree with you about the fandom, I guess 80% of them doesn't even understand the series. Here in my country it became really popular among incels(due to a bad scantranslation) which is stupid because Fujimoto has some leftist tendencies. In his other work(Fire Punch) he talks about themes like transsexuality, totalitarianism, religion etc.
But don't take me wrong, Half of what Fujimoto draws(specially in CSM) doesn't have meaning and it's just him having fun with bizarre stuff and film references(like Sharknado)
If someday I write my analysis about the series I'll tag you :)