It's not that the MVC is wrong, it is that the model is not being built right. Moving to the BorrowABook feature is making a model class.
All too often in my experience I see code that has the model rolled into the controller. Controllers and UI are structurally supported better in frameworks. We get lazy and put model code into controllers. It is the way we make spaghetti code today.
We get lazy because most of the time ,without a proper Ioc container , writing code the right way is too much verbose.
Ioc containers changed the way I code since I did not have to care anymore about how complicated it was to instanciate objects. It helps write very clean code and makes OOP easier.
All too often in my experience I see code that has the model rolled into the controller. Controllers and UI are structurally supported better in frameworks. We get lazy and put model code into controllers. It is the way we make spaghetti code today.