Obviously there's ooc RM just as well & I don't claim even my own RM is necessarily ic.

That said, gonna be mean about MR for a hot minute, fair warning.

Because overall, I agree.
It's usually Mob's portrayal in MR I grapple with more, yeah. Not because he's made to be muscular, that part has a hook in canon & his training is an important part of his growth, so wanting it to bear fruit is something I can get behind.
But really most of it seems to come down to stripping Mob of everything Mob, only to create a stereotype around that aspect. And let's be honest, if we have to pick a stereotype, he'd def have to be a himbo - he's already a little dense & very kindhearted, just the physique is lacking, so...

The ending of the show is really important to me personally & more often than not MR strays in the exact opposite direction of all that ending tells us, which makes it unenjoyable for me. So yeah, absolutely agree, even if set in the canon universe and not explicitly in AUs like Ageswap etc, MR seems much more often like an exploration of canon divergence!
And that's fine ofc, fanwork is inherently wish fulfillment territory, but personally I'm just more interested in the expansion of their specific canon & that's much more easily to find in RM.

Which saddens/frustrates me sometimes, because I don't hate Mob topping at all & I don't hate Reigen bottoming for Mob but the execution puts me off most times.

That said, I'm also just incredibly picky anyway, though. Which goes for both RM & MR, I've read more than one RM fic where Reigen suddenly got a little too stereotypically (<- keyword) sexy for my taste, it just happens less than in MR (& in MR the "sexy"-curse hits both of them, in different ways) & I'm def more lenient with it in RM too, simply because RM still usually has tropes I can anjoy for the horny at least.

Aaand I realize my tweet was about art but I'm much more talking about stories here, whatever.
& of course final disclaimer, there's MR artworks I love (yet to find a fic lol), not all MR is ooc etc etc, these statements are not universally applicable & only my own opinion yada yada. Cheers!