Freak athletes are not all the same.
Cook is big and fast. However, he is not really explosive. In other words, it takes him a bit to get going off of the line. Also, he lacks a real change of direction type athleticism. He is a straight line speed kind of guy. So, he can be kind of "clunky" when trying to change direction or do thinks like block. His on field awareness is not always the best either....holding the ball out away from his body, getting stripped from behind ect.
All of that said, in the right O with a QB like Rogers I am sure he could put up good TE numbers.