Thats why I said your statement of PIN being more secure is up for debate
And if someone does know your PIN or its compromised (not guessed) then the phone can be unlocked ...... much like the PIN on a bank card its only as secure as the user or the environment the user is in (eg being filmed using the bank card or phone PIN), how many people use the same PIN for both bank card and phone ? One compromise potentially gives you access to both.
I've not heard of many ways to compromise someone's face (and yes I know you can compromise faceID while someone is sleeping) but that also involves physical possession of the device.
It's an interesting debate