I could sort servers on the joinmastodon.org list by proximity to 150 active users (Dunbar's number), I don't know if that would be an improvement. The working set is still 60 top active ones in each category.
For example, sorting the "I am ..." set like that puts writing.exchange, lbgt.io, and monsterpit.net on top, and mastodon.social on the very bottom
On the other hand I do not see a compelling argument for why exactly Dunbar's number (number of personal connections you can maintain in your life) should be used. I don't think most people go into social media expecting to know every single person on their server, and having a headroom of people you don't know might even be a positive thing.
Invite-only Mastodon server run by the main developers of the project It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!