I think the logic goes something like this:
Apple is a trusted brand for privacy. Even if FaceID is harmless in terms of surveillance potential, it still associates positively in the minds of users, such that when other vendors — or even the government - decide that they want to use it to, and not with the same on-device protection, etc - people will accept it willingly because it was safe when they did it with Apple.
I agree with other commenters here that these arguments lead to a sort of infinite regression. All of the things Apple has implemented is rather old tech by now. If we accept those as surveillance, we practically can’t have anything. Which sucks.
Apple is trusted now. But they might not always be. They could go the way of their competitors. Then where would we be?