Do we agree that Book has good form on his throws? He scrambles pretty well once he decides to, although many if not most of the times his decision to is the wrong decision.
How much of his poor play is that he plays scared? Or anxious. He is not patient.
He is probably playing under pressure to be better and is not handling that well.
He should be learning something after every play. If he can't shake the pressure to be great, he won't be great.
If he is a great or even a good QB in the growing stage, he should be showing more fruit of that inner talent by now .
It is possible that he is a late bloomer.
I say that because he does show signs of being good.