No. Passkeys parasitize on FIDO2 U2F standard, that was developed to be (as the name implies) the second factor. Resident keys are meant for on-device 2FA with PIN, a functional replacement of smart cards.
Someone (Apple maybe) thought it’s a good idea to consider WebAuthn being good enough to be the only authentication factor (no resident keys, no hardware bond, keys are roamed via iCloud) but TouchID/FaceID protected on device. And they branded them as passkeys.
> and for that you probably want the 2-factor properties afforded by phones or desktops which usually require "something you know" or "something you are" to unlock in addition to the "something you have" afforded by physically possessing them.
You don’t. 2FA is not a goal on itself. The goal is to have user authentication that is protected from phishing, brute force and credential stuffing, and also not as hard to implement as smart cards.
FIDO2 does that. The problem with Apple’s, Google’s or Microsoft’s implementations is not that they are less secure on a protocol level between the authenticating site and the user’s device, that’s exactly the same protocol. The problem is that the site has now to trust user’s personal account in one of these platforms and that the user did the right thing and also the platforms will always be doing the right thing - e.g., they will handle attacks on user’s personal account properly.