And they absolutely should not scale. Scaling is the root cause of all social media ills. If all you see are the 100 people nearest to you, the village idiot will not be able to spread his gospel so easily
No mixing between known users (friends, followers etc.), recommended users (swipe feed) and advertised content.
No publication of user content. It's social media, not global media.
I posit that these points will be enough to curtail most of social media ills. Don't allow recommendation of slop and there will be a similar reduction in production. There will still be the village idiot that shares slop content, but their reach is limited since they have to actively persuade people to their message, rather than be recommended for being psychologically stimulating.