> Passkeys don't offer portability, user choice, or user control.

This is objectively false. Every major platform provides user choice in Passkey Manager. It's the same flow/settings to setting up a third party Password Manager.

All of the ecosystems have defaults that include some amount of portability: iOS defaults to Passkeys synced through iCloud Password Manager and backed up/restored with device backups. Android defaults to Passkeys synced through Chrome Password Manager. Windows defaults to Passkeys synced through Edge Password Manager. All of the ecosystems have plugin systems to support third party Password/Passkey Managers such as 1Password or Bitwarden.

Most devices that support Passkeys support a QR code bootstrapped flow for cross-device/cross-ecosystem Passkey challenge signing via Bluetooth LE.

Most ecosystems deliberately don't provide explicit private import/export to help protect users, but that's more an implementation detail than a technical requirement, and mostly not an implementation detail for "lock in" reasons but for simple security reasons: the private key you cannot export is the private key that is harder to steal by bad actors. The private key that you cannot manually import is the private key that can't be installed by bad actors.