Well you neglect that from what we know now it will most likely become reality that we can backup/sync passkeys across private clouds/backup solutions/authenticator implementations as well. And that makes them really strong for those who want them to be independent of third party cloud provider or vendors. Just like OpenSSH Agent is for decades already and at least I was always wondering why not brining something similar to websites (actually using just that would have worked too but WebAuthn has some extras which I would not need but which are okay I guess).