Anime twitter is just being honest

DS is not that special
In terms of what is amazing in DS imo is the character design (the characters have insane drip) and the animation in combat. The issue is i feel no investment or attachment to anything that happens.
I got shytted on multiple times for my view on DS but people are finally seeing it as i see it.
MHA is a funny case. The show leads you to believe its the GOAT shounen at first but stagnates multiple times which is what is causing this turn. It does some GREAT things but also on review or second watching you start to notice the show hasnt done as much as youd think.
I personally still like it for what it is. The next couple arcs more people will come for MHA is my prediction. I think its fine for the face of modern shounen though.
I see what you're saying, but I don't think DS has to be special to be loved the way that it is though. And even though it might not be groundbreaking in storytelling, I do think there's a lot of elements to it that does make it stand out. I mean technically, Demon Slayer is very similar to Bleach, if Bleach had an
extremely nerfed cast BUT to some... That's a good thing.

Switch out demons for Hollows, Demon Slayer Corps for Soul Reapers, Nichirin Blades for Zanpakutos, Breath techniques for Reiatsu/Reishi/Reiryoku abilities and there you go. It's not a rip-off of Bleach, but there's certainly parallels. Even so... Demon Slayer isn't what I'd call generic either.
Take DBZ for example. Dragon Ball Z's story every time is, "Guy threatens Earth/Galaxy/Universe/Multiverse, ends up killing or seriously wounding some of Goku's friends, Goku achieves a new form and Vegeta is once again in second place." But that doesn't make it any less captivating, at least, to plenty of people you ask. People had their issues with Dragon Ball Super, but it was mostly either the art style, the power-leveling scale (Kefla angered a lot of folks a couple years ago

) and the writing for characters like Jiren. Other than that, most people still enjoyed Super as a whole. And if Toei brings back Dragon Ball again, it'll once again be one of the hottest anime being released weekly.
But even if in the case that DS isn't special, it still doesn't earn the hate it gets. Anime Twitter would make you think it's on par with Sword Art Online, and I guess there lies the reason why people don't like it -- because for many people, Demon Slayer is their gateway into anime, so because it's "surface level", it's somehow "bad". But you know, there were people had the same sort of energy for Naruto and Bleach back then too. Sword Art Online is also entry-level as hell, and while I'd never say it's the best written series out there... It's nowhere NEAR as trash as some people make it out to be. (Even though Alfheim Online was weak)
My Hero Academia, Demon Slayer, Black Clover... While they probably aren't reaching The Big Three-levels of popularity, I think they're serving the same purpose. MHA isn't better than Hunter X Hunter, but people are going to gravitate to MHA for a bunch of reasons. It's the same reason why newer younger fans are going to check out Darling in The FranXX before they check out Evangelion most likely, or Kill La Kill before Gurren Lagann -- it's what's current (or more recent).
Hell, one of the biggest Shonen series in that Jump magazine is about high school volleyball.

Let's not forget that for the past year and some change, we've been getting hit with isekai after isekai nonstop.

So it just goes to show, people like what they'll like. Shonen just happens to be the one that people get into easier.