As a little extra, android sets 3 levels of security for biometrics.
Level 3 is trusted for unlocking apps and banks. This level has to have the code entered every 72 hours. Aka samsung fingerprint
Level 1 and 2 are weak security and cannot unlock apps, these are more for convenient screen unlocking. These reset after 4 hours of non use or 24 hours of time. Aka samsung face unlock. Face unlock with a single camera as you said isn't secure.
To have face unlock for apps and banks, samsung would need to make a level 3 face biometric. Something that as you said, would need extra sensors.
Thought this was interesting as the 72 hour and 4 hour thing isn't set by samsung, android themselves set it