Considering that Apple has opened up third-party apps to do autofill for things like passwords (I autofill password fields from Bitwarden on iOS all the time),

Considering that Apple has opened up third-party apps to do autofill for things like passwords (I autofill password fields from Bitwarden on iOS all the time), this seems a lot less like an advantage they're gating to their app and more like a potential feature they just haven't shipped yet because it has no use case at the moment (since right now nobody sends 2FA codes over any platform other than SMS). If it became widespread to use WhatsApp, Signal etc. for sending 2FA codes, I'm pretty sure Apple would add it. There's not really much other system integration with iMessage either, other than some Siri stuff I doubt sees much use. It's surprisingly disconnected from the rest of the operating system.