In the sense of "I refuse to support browsers that only support tls 1.0", definitely. "Just let the user turn off TLS, why do you hate choice" isn't the instant win you might hope it is.
No, again, the protocol between the site and the authenticator is unchanged.
It's much more like DRM that doesn't let 4K media play on systems that allow the user to do whatever they want, but in this case instead of the DRM preventing the user from copying someone else's copyrighted work, it's preventing the user from copying their own data.
I agree that it's not an unqualified win. If sites block passkey apps that allow exporting unencrypted passkeys, that probably will prevent some accidental passkey leaks.
It's just that it's not an unqualified win to allow sites to block passkey apps either. If we allow that, we can get to a place where sites block apps for the wrong reason, or it becomes more expensive to develop passkey apps so there is less competition for secure passkey apps.
It's not just whether it's a good idea to allow unencrypted exports. It's whether it's a good idea to give websites a say in how we manage credentials.