Nostr's relays are simply servers that push and receive structured data. So it's a sort of an email or http like protocol that's by default cryptographically signed? I don't really see the magic that makes it censorship resistant or particularly decentralized. The same networking and economic laws that consolidate internet traffic or mastodon servers are at work here too. Relays get popular, produce a lot of traffic, this spawns "nostr as a service" for economic reasons, and that's about it.
If people want to ban you they'll just blacklist your public key across popular instances just like someone on the fediverse does, companies won't host your stuff, and so on. If anything tying everything to a single global identity makes it more trivial to blacklist anyone.