I agree that the poor design of the passing game is a chronic Kelly issue and limits the offensive output. I am not "down" on Book who does well with what he has but his lack of arm strength is visibly apparent when you see it live against talented teams like USC and limits the offense even more.
The problem for me is that if Book is the "best" qb on this roster next year, it shows an extreme lack of getting the right qb and/or not developing the qbs we do get. If we have a stud running game, we could get away with a qb with Book's arm talent. But as you will see with Wisconsin when they pay OSU, an average qb only goes so far at the elite football level. We will never really compete for a NC with a qb with the overall talent level that Book has.