Doesn't being able to sync your passkeys by entering your conventional password somewhere eliminate the whole point of passkeys? It just shifts the point where you can enter the password to recover your data to a less convenient place. And if your entire stack is passkey-protected (which I'm pretty sure is the case most of the time) then the secondary phone won't do anything for you.

When I said "survival", I meant it in the "being able to make do with few resources in a time of crisis" way, not that you will literally die if you can't access an account. Losing a crucial device without a fallback of being able to log in somewhere else quickly can mean immediately losing access to payments (the most crippling, especially if you're not home), being stranded in an airport or even not having an identity document (in countries with digital ID systems). Any of these happening can lead to enormous losses in time, money or worse, depending on when and where this event hits you.