Maybe I am over estimating it....getting some "blur" when I am stopping it.
At any rate, I would not say there is "no" external rotation, there is some.
I don't see 80 either.
I stand by the shoulders being closed at foot contact. But, there is not much happening to involve the body.....kind of opens the front leg, lands and throws all arm. There is an element of some of shoulder rotation.
But, I am not a real "mechanics" guy....so, that is worth what it is.
I would not expect an 8th grader who is 5' 7" to throw 80. If Mr. Walker is I am stoked for him as it would put him in the higher level velocity wise. But estimating velocity is a bad habit to get into. "Around 80" can end up looking a lot like 71.