Yeah, and would you like to be treated by a doctor who has only used Passmedicine, which is their equivalent? I don't think so....
You do owe a duty of care to your future passengers, and the authorities will ask schools about students who have had accidents. I had such an enquiry just three weeks ago.
It is true that some of the information at the start of your career may appear to be irrelevant, but you will need to know it by the end of your career, and for the tech interview, at which they will not be asking multi-choice questions. You will look a complete dork if you don't know your stuff - to quote a flight school who rang me up one day about someone who had turned up for training "is it possible to pass the JAA exams and still know d*ck?". The FAA know this, but allow you to learn it as you go along.
And for your information, Negan, I was using convergency and conversion angles when flying around large open spaces, such as the North of Canada, as were many of my colleagues, not to mention doing my own weather forecasting because you are out there on your own. Ask the people whose navaids suddenly don't work in Africa or who have to get through to the base using HF, which was still being used over the N Atlantic not that long ago.
And you won't learn a whole subject through the QB - only that stuff relevant to the questions contained in the database. The QBs are useful for consolidating the knowledge you acquire in your studies (assuming the study material is up to scratch - much of it isn't) and getting used to the style of questioning, and some of the quirks. Period. You need both.