I understand your point. Frankly fingerprint readers sound iffy to me (see previous research on spoofing fingerprints) and Face ID et al give me more concern because in theory someone can just take your phone and point it at your face to unlock it. I’m also not a fan of using biometrics for “locking” Android apps (see recent versions of Signal), and it should NEVER be used to retrieve a decryption key from a “escrow” chip for a full disk encrypted device (just a hypothetical scenario I’m sure someone’s thought up)
I think the whole reason Apple invested in implementing biometric (Touch ID, Face ID) based unlock on the iPhone is because they assume their userbase isn’t intelligent enough to handle a separate FDE/preboot and lockscreen password and the biometric unlock is to mitigate having to put in your password many times per day. It goes without saying you should have a long enough FDE password, but if file based encryption to protect data from a decrypted but lockde device is going to be a feature the security of it depends on the complexity of said password as well. I don’t know how Apple handles this with Touch ID, although I suspect its “have the key in a “escrow” chip to “release” the decryption key upon biometric unlock and hope for the best”, so that’s a concern as well.