@PlutoniumAcid first of all, you would go by most active not biggest subscriber numbers (which you can't actually see accurately from within your own instance), and not everyone even does this, let alone joining everything.

Recently I made a multi for news communities so I could get an overview, and it's definitely not all the same people in all the big ones (my instance lets me see the names of upvoters). People join what feels right.

I don’t want to bother posting on all the damn sites.

I don't get what you mean by this. I post all over the fediverse but I do it all from right here on kbin! That said, there's no need. Why not just post in the communities you like most? It's no different to reddit in that regard - you don't feel pressure to post in all the subreddits, do you?

Eg outside my own instance I like the big movies over at .world but when it comes to global news I prefer .ml, but for sciencey stuff I tend to sub on mander.xyz.

but it’s juuust shy of being mainstream enough for the average Joe

True, for now. Full disclosure, I don't particularly want reddit to move here just yet. It was getting too full of people who sound like my racist aunt. The fediverse has a feeling of chill still, people contribute because we're having fun building something new, there's no algorithms, shill armies, or enshittification.

I've been on the internet since the 1990s, so I've seen things rise and fall, and I think the future of social media is federated. I get enthusiastic about it, but of course it's not ready for everyone yet, and realistically most older people may never even get here. But now I've discovered it, I'm never going back. :)