The expectation is that for any service you should be able to have multiple passkeys -- including multiple passkeys from different vendors. I'm not sure how that exactly causes lock in?
That misses the overhead of having to rotate the passkeys for thousands of websites you've used them on.
Exactly, you can just register passkeys from multiple providers if that's a fear. Worst case (i.e. Google nukes your account and you've only set one passkey), you go through the usual email recovery or backup codes process and set a new one.