But they’re not the only one using passkeys. If you could have multiple passkey logins to an account, it’s not earthshattering if one of them becomes unavailable.

That's the intention yes, and it's a whole 'nother conversation about how many passkey-eligible devices people actually do have in reality, and how often they travel with all of those devices on their person at the same time and how often they're going to actually go through the extra steps of logging in on their secondary devices and adding a new passkey.

My parents are a good example of this, they have recovery options set up so that we can get into their accounts if they die. None of those recovery options are compatible with current passkey implementations, and their phones might be the only computers they have that are capable of storing passkeys right now. I myself have exactly one device that's capable of acting as a passkey authenticator right now (my phone) and I suspect that'll stop working if I De-Google it and then I'll have zero usable authenticators. I'm not sure how I would add redundancy to a passkey login without buying additional hardware. It's not like my password vault where I can sync it to basically any computer or flash drive.

But that's a separate conversation. Regardless, the goal is the elimination of the password, a lot of coverage and advertising has centered around that. Passkey isn't in the long run designed to be supplemental to traditional log-in methods, it's intended to replace them.