A site having the technical ability to determine not just its authentication mechanism but how that authentication mechanism is stored is not its choice and should not be its choice and is not its business.
And its a clear degradation in user freedom over passwords, a system where it's impossible for Google to dictate that you use only a specific password manager to store and sync that password. It shouldn't be possible for Google to know how I'm storing a passkey.
It's not their right to decide anything about that. They've never had that right. We're not taking a freedom away from Google, we're saying that Google should not have the ability to take away a freedom that we've always had, because they're our devices and it's our login information; it doesn't belong to Google.