@tarkowski I don't remember the figures now from the instance distribution paper that was written a few years ago, but I think we're not too far off if we say 90% of the people on the network are on big servers like mastodon.social, mastodon.online and pawoo.net, 9% are on servers smaller than 100k but larger than 1 user (and probably hosted on Hetzner in Germany or Finland), and 1% are on single-user servers (hosted in wardrobes everywhere).
That's probably pretty ok in terms of diversity. The potential for personal expression and creating one's own experience is there, both technologically and socially. The most valuable innovation in e.g. GlitchSoc is upstreamed to Mastodon eventually, and cultural norms have a similar pattern. There is a safety valve so the the almost-centralized part doesn't become a walled garden.
Plus, rather importantly, the major part of the center is run by a gGmbH, not a corporation with rent-seeking investors.