ND's model is to recruit a stud every third year or so. It's hard to get a top-tier QB every year, because all HS top-tier QBs think they are going to play in the NFL. To chase their NFL dreams they need to play in college, and so they are constantly looking at schools' depth charts to gauge their chances of getting playing time. Wimbush was a stud QB recruit, which is why we then had three-star recruits Book and Avery Davis for the next couple of years. Then we recruited Jurkovich as a stud QB recruit, which means that we will likely have a couple of years where we will have to settle for three-stars. This isn't to say that Ian Book, a three-star recruit, is no good, but it helps to explain why we don't get 4+=star QB recruits every year.
I think we have seen Book's ceiling. Nothing against him, but he isn't in the same league with the starting QBs at Oklahoma, Alabama or Clemson.