I didn't read the full discussion, but npubs are definitely insufficient. That's why we have nprofiles, nip05s or at least the dependency on a client having access to a greater ecosystem of recent events from other people that may provide updated hints to the relays of a bare npub, ideally through some form of local database. It's all on a best-effort basis, no mathematical guarantees, but I think that suits the messy world we live in very well.