That's a measure of success that makes sense only in a for-profit, growth-oriented environment. Software just has to be sustainable and "bigger" doesn't necessarily imply "more sustainable.
That said, what is now possible with social media is extremely restricted and our idea of what a social media is is constrained by profit motives. Social media could be much more, connect humans for collaboration and exchange instead of data extraction. We are so used to the little crumbs of positive experiences on social media that we normalized it.
Bonfire, for example, if we want to stick to the fediverse, is trying to challenge this narrative and push the boundaries of what a social media is supposed to do.
Another space would be non-siloed notion-like tools.
Anothe entire can of worms would be to go beyond the "dictatorship of the app" and start building software and UX around flexibility and customizability for the average user, rather than keeping this a privilege for tools targeting power users. Flexibility in UX means harder trackability and less CTR, so most end-user "apps" avoid that.