I already saw this happening on Reddit. The largest subreddit were filled with generic posts. They got a lot of content, not necessarily good content. But there were plenty of small or medium sized subreddits that had much better content. The Fediverse feels like it is missing the big subreddits. It also feels too small to have the small niche subreddits. What is here in terms of content feels more like a few medium sized subreddits.

This is a good point. My interactions with the Fediverse over the last few months has been sublime. Maybe users here are just proportionally more active?

Numbers are nice, but they're not everything. Yeah, we could onboard 2 billion lurkers, but how would that improve anything?

You're unlikely to be in conversation with hundreds of millions of people at a time; or even thousands of people. Conversations happen with just a handful of people. So those platforms with billions of people perhaps allow for some ultra-niche subgroups, but otherwise are just providing a lot of low-value noise with the additional people.