How Detailed Should Biographies Be? Paul McCartney for Example

I took out the biography shown above from Queens Library.  It took me almost three weeks to read the 800+ pages that cover Paul's life from birth to 2016.  Philip Norman is a noted British writer who has written biographies of Buddy Holly, Elton John, Mick Jagger, and John Lennon.  He states that during the three years of researching the book he had access to McCartney's family, close friends, and associates who otherwise would never have spoken on the record.  I enjoyed reading the book since I stuck with it for 800 pages.

I am aware of another biographer of Paul covering only 1969-73, the beginning of the post-Beatles era.

Kozinn is a former reporter and critic for The New York Times, while Sinclair is an English documentarian.  I have not read this 700-page tome that covers only five years.  I question whether this book includes many minutiae that would only be of interest to Beatles scholars. I obviously don't know since I have not read the book.  I suggest my readers consult the book review in the New York Times.