Ordering a conversation between an unbounded set across independent nodes leads to misordered interactions not possible if you just centralize. It seems like a small issue, but at scale quality really suffers when some universal, fine-resolution ordering can't be agreed upon.
You can devise many clever schemes to try to avoid centralization and achieve coherency, but if one service is more up to date with more info, it is preferable and offers a more coherent public conversation. Network effects still dominate despite the protocol.
All that said, if I wasn't very aligned with the spirit, I wouldn't care so much to think about it. I'm also aligned with the spirit of Bitcoin but the culture present in both doesn't help it. The fact that Nostr is Bitcoin aligned, meaning it rejects the technical options of protocols taking more risks, hurts it.
The way it handles public keys and identities is very simple and good and to me is very obviously reflective of a good future state. But it's not unique to Nostr.