I read most of the book. He mentions Brian's rap on "Smart Girls" as an example of advanced genius (which he seems to define as expressing yourself in the most real and comfortable way possible with no concerns about how it will be critically or popularly received). However, he purposefully avoids analyzing Brian's entire career, instead analyzing the careers of other rock stars (like Lou Reed) that fit his theory better. Brian's career, with the release of songs and albums like "A Day in the Life of a Tree", "I Went to Sleep", & Love You, is inscrutable. Was he going for popular reception? Critical reception? Pleasing his own muse? You can't really say for sure.
I knew there wouldn't be a whole lot about his career, even though to me, I think there'd be a lot of material to say, "Brian, are you mad? or is he just ahead of his time?" and the latter will be your answer.