No group is unanimous and completely homogeneous. But judging by how often the security benefits gets brought up by those in favor of passkeys in these kinds of discussions (including this thread), my impression is that most of its advocates view it as a security benefit. Which means they need to replace passwords, not be an optional extra.

For important sites like your email you'll add multiple passkeys. On less important ones you can just reset which passkey you use to login, using your email, if you lose one of your passkeys.

That doesn't help with the posited example of "I lost my phone and need to borrow someone else's computer".

It does. You just use one of your other passkeys, like a hardware token.