Kris on Nostr: I don't quite agree. Yes single-user instances are at a disadvantage, but so are huge ...

I don't quite agree. Yes single-user instances are at a disadvantage, but so are huge instances (for multiple reasons). What ActivityPub actually encourages are medium sized (few hundred users at most) instances that have a meaningful local feed and sufficient connections to be seen more or less everywhere. It is not so easy to get there starting out as a lone user, but I think the idea to encourage people to host services for others who might not be able to do so is a strength of federation.