> Seems like vendor lock-in was the goal from the start.
Exactly. The passkey vendors state that the goal was to make phishing not just difficult but impossible. This means plaintext access to your credentials is forbidden forever, regardless of your level of expertise, and regardless of the complexity of the process to export/import them. The purpose of the so-called "secure credential exchange" is once again to prevent you from directly accessing your credentials. You can go from one passkey vendor to another, but you're always locked in to one passkey vendor or another.
Any credential system that makes it impossible to write something down on a piece of paper, take it to a new computer, and login to a website is just a gateway to vendor lock-in. You can manually manage your own ssh keys but for some reason not your passkeys.
As an Apple Mac user, what annoys me the most is that the use of passkeys in Safari requires iCloud Keychain, which of course requires iCloud and an Apple Account. [EDIT: Obviously I'm talking about built-in support. I'm well aware of third-party software, so everyone can stop replying to this now, please!] You can't do local-only passkeys, not even if you take responsibility for backing up your own Mac.
The passkey vendors took some good theoretical ideas, such as site-specific credentials and public-key cryptography, and totally mangled the implementation, making it hostile to everyone except themselves.