I’ve read horror stories about losing or breaking a phone and being locked out of everything because the standard phone backups don’t save the passkeys private keys.

This is no different than what we already have. Many people don’t backup their TOTP to any cloud provider, or even themselves, and if their phone breaks, they lose all of their TOTP. And most people don’t save recovery keys (if the service even provides them).

So ya. Stop fear mongering.