- User accounts are tightly coupled to a single key. There's currently no account abstraction.
- Nostr is tightly coupled to a specific crypto primitive and doesn't attempt any sort of crypto agility.
- The plan appears that user names are delegated to the centralized DNS system (https://github.com/nostr-protocol/nips/blob/master/05.md)
DNS is not centralized, it is distributed. A name server can delegate authority to other servers. Every nation has their own, which I consider sufficient decentralization. (Although it does rely on IANA to list addresses of root name servers, which is perhaps the centralization you refer to)
Do you propose another naming system?
There are alternatives like ENS. I don't mind Nostr just simply having its own system.
There are the universally accepted root servers, ICANN, national registrars, etc.
But nothing prevents you from trusting additional root servers, with TLDs if your choice, delegation of subdomains from them, etc. All the standard mechanisms will just work. Your router likely supports the .lan TLD out if the box.
DNS the system that we all depend on depends on the assumption that we all use the ICANN root servers.
I would say there's still some degree of centrality for ENS, but it is more decentralized than DNS.