It's worse than motor memory (no thought required) gesture, because it requires a more expensive non-motor-memory physical movement that depends on context of the human. Face ID requires moving and orienting phone close enough for the Face ID sensor to capture a 3D image of face and moving eyes for attention, so it's a function of both phone and human position.
TouchID is context free: grab phone and touch button in fixed position. By the time the phone has turned to facing the user, it is already unlocked.
