Your synopsis of Book’s “perfect storm” is spot on. Those skill sets really compliment each other nicely, supported by tremendous instincts.
They kind of need to. Book knows he can take his time and be more cautious, maybe because there's that sense that he can usually make something out of it with his legs if nothing else, avoid costly sacks etc. You just can't afford to hold onto the ball as long as Book often does if you're getting sacked and having too many negative plays on account of being slow of foot.
They were comparing him to Fran Tarkenton in the broadcast. Nice!
Here's sr year highlights of Brendan Clark if you're interested. I kind of feel like saying where Clark is concerned, that if Ian Book can do it, why can't someone like this guy? His profile is not that dissimilar to Book's.