>"Consider a user in the Apple ecosystem"

Already you're off-base. Of course it works when your devices are homogenized, but very little folks work that way. Some people have a Windows computer using Brave, an iPhone using Safari, an Android device using Chrome, and a work computer with its own hardware/software limitations and partitions.

Of course it works when your ecosystems are not diversified. Problem is, most people are.

Even using passwords instead of passkeys is going to be a worse experience when using different platforms like you mentioned - I have a massive number of passwords from recent decades.

A cross-platform password manager like Bitwarden handles passkeys (and passwords) across multiple operating systems, browsers, etc.