Passkey is some sort of specific unique key to a device allowing to use a pin on a device instead of the password. But which won’t work on another device.
Now I don’t know if that key can be stolen or not, or if it’s really more secure or not, as people have really unsecure pins.
It doesn’t feel better? Good thing security doesn’t care about feelings. The fact is it is more secure no matter what it feels like. Privacy is maintained since you use a new key with each site. There is no IMEI or anything like that in the passkey spec. Social engineering ranges from more difficult to impossible depending on if you use a synced, local software based, or hardware based passkey system.
You have a lot of incorrect assumptions. Read https://support.apple.com/en-us/102195 and https://fidoalliance.org/passkeys/#faq.