You know what, you've convinced me. I've been rooting for some kind of society-at-large network to succeed at federation (I was so optimistic I tried bitclout, and more recently bluesky. Both want to be a single global database to send money or to index hashtags and blocklists globally)
I really believed that discoverability is king, and I should just be able to search a global graph of user profiles and read everything that everyone has ever said, but you're right, there's a lot of conversations that don't happen in public, and not everyone wants to be "discoverable".
So I think there's a case to embrace the balkanization of social media, and go back to having separate identities to be a part of each phpbb we signed up to. Going to different domains to talk to different groups of people makes sense, and we can have the modicum of privacy offered by a semi-private chat server like discord, so that your messages don't get indexed by google and archived forever. (Obviously discord retains all the message logs, DMs included, but at least its not publically searchable)
And global social media is always going to suffer eternal september. Smaller, unfederated chat communities is a probably a much healthier approach to social media than whatever it is we've been doing the last decade of meta-gramming