I agree. There are levels of resistance.

Some protocols with high censorship resistance detect and route around censorship, blind the end nodes involved, hide communications steganographically, etc... nostr doesn't do any of that.

But beyond being decentralized, it is organized to rapidly and easily switch providers (relays), on every note you post if you want, unlike older decentralized protocols like email or UUCP, along with expected redundancy of posting.

So I'd call it fully distributed and somewhat censorship resistant.

Not being able to distribute a client through a walled garden isn't a fault - no client could possibly do that without the walled garden's approval.