I believe social media apps are much like markets, in that the structure of the app determines the incentives and the interactions that happen there. I think most would agree that the 140 character limit had a profound impact on Twitter, for better and for worse. This is why HN remains stripped down, without Reddit features like message alerts and visible karma for posts, and why the lists were stashed away; these features don't work towards curious conversation. The things you're citing about group chats are structural, as well.

We aren't doomed to terrible social media. But tech companies, with their particular incentives to drive engagement writ large rather than healthy engagement, may be structurally unable to deliver a good social media app.