It would be interesting to verify this. Nostr likely does have a power law distribution of users to relays. Preferential attatchment describes that when new users join a network they will join in a biased way, connecting to their friends and those that already have an established presence. Considering that Outbox isn't widely used, that many of the onboarding clients use their own relays, and that general users would be less likely to change their relay settings unless told to do so, I'd expect that we're still very centralized. Key factor - microblogging incentivizes following users, not content.