Hasn’t every form of social media done this though? It’s on the users to collectively shape the culture of a site as a whole. For example Hacker news manages to maintain its ultra nerdy niche through the years, because the users keep it that way.
For years I’ve had two separate Reddit bookmarks on my toolbar, one for r/all and one for my homepage, because for me those were two completely different experiences. Reddit has both shitposting galore, and also (had?) r/AskHistorians. It managed to be both, and Lemmy can do that too.