I don't think this is true. If I open my wallet from the lock screen then cover the front camera and close the wallet app my phone remains locked. Obviously it's a different story if you open the wallet app when the phone is unlocked
That being said, I do have some non-default FaceID settings

I completely agree. I guess you can turn off biometrics if you're in an environment where being forced to unlock your phone is a threat ( airports would be one of those envs for "normal" people ) but most people aren't going to do that