While Book's long range passing is still a question mark, his short range and medium range passing are fine. The key here, is that he can still stretch the field vertically with the medium range passing game, to the point where they can't simply squat in a short zone like our opponents were doing in 2013 when Tommy Rees was at the helm.
Rees didn't pose a medium range threat when it came to passing, which was why teams could simply drop 8 into a short zone coverage, and try to jump the routes.
Now, that being said, yes, it would be quite a boon for us to stretch the field vertically with a long range passing game, so that squatters could be burnt, and that would certainly open up all of the offense to be used effectively.