> All these answers above depend on the login system being well designed. If the people writing the website don't let you register multiple passkeys or don't make it convenient to register a new one whenever you login on a new device, or don't offer the aforementioned Qr code login system or don't offer good account recovery - you will have a bad experience.

But this is one of the points being discussed here. All of depends on a large number of choices that each site owner will have to get right. You could always argue "well, it's the site's fault for not doing it better", but the matter is that the site owner has to decide those things at all - and if course they will make their own tradeoffs or simply don't bother with certain features.

So you will always have a wildly inconsistent mix of different functionalities and constraints depending on the preferences of the individual services.

Whereas with passwords, implementers don't have to do any of those choices, the basic implementation already supports all those usage scenarios.

The QR code login flow is one such example. I probably have some bias that I don't like the thought of making my phone the sole authority for all my accounts, but even if you accept that, it's an exotic technically complicated flow for the exclusive usecase of "login on untrusted device". There are probably few sites that weigh that usecase high enough to implement the flow - whereas with passwords, there is nothing you have to implement, because the functionality is just a natural consequence of how passwords work.

> Whereas with passwords, implementers don't have to do any of those choices, the basic implementation already supports all those usage scenarios.

Sure, in that sense the usability is better, but now we are dependent on the website makers to make choices on security (offer good 2fa, don't limit passwords to 8 characters and store it on an ancient mainframe, etc.) and even then the usability can take a hit if the website is ignorant of or actively hostile to password managers (breaking autofill and such). Neither system guarantees a good experience.

With my example I tried to paint what a good passkey system would look like for OP, I am aware that leaving the usability part up to the website will result in such a mix.