We don't have all of the options available to us with Brandon Wimbush at the helm, especially when the offense absolutely must have an accurate short-range passer when it comes to red zone work. One of the most powerful red zone weapons is a play action pass to the TE, and if he can't complete a short range pass reliably, then it becomes more likely that such a weapon becomes a dud.
Ian Book has shown that he can make those short range passes, which actually opens up more running opportunities, since the field gets truly spread horizontally.
Also, I'm not entirely sure that Brandon Wimbush has improved upon his ability to make pass protection audibles. With his mobility and running strength, he probably doesn't need to do so often, but if he wants to survive the whole season, he'd better show more proficiency at that.