So far I've found it useful, I'm not that far through it though.
He kind of touches on that as well. He likens it to (before the days of online reviews and such) the way people decide what they're going to watch at the cinema on a Friday night is they'd look in the listing in a news paper where you had a few lines to tell you what the film was about. Hundreds/thousands of people submit ideas every week, and each one of them basically has a few lines to "sell" the idea (known as a logline). Apparently a large % of spec writers are not very good at that part of the process. If you can't get people interested in your original idea in a few lines, it's never going to see the light of day.
I think the reason the movie going public isn't asking for more variety is because most people don't go to the movies that often. When people do go to the movies they want to see something that entertains them. It probably doesn't matter to them that 50% of the movies they watch are superhero movies, as long as the movies are entertaining them.
If you look at it from the perspective of a casual viewer, you want to go to the cinema Saturday for your monthly/bi-monthly cinema trips you see 2 options.
Option 1
The Lost City of Z tells the incredible true story of British explorer Percy Fawcett, who journeys into the Amazon at the dawn of the 20th century and discovers evidence of a previously unknown, advanced civilization that may have once inhabited the region. Despite being ridiculed by the scientific establishment who regard indigenous populations as "savages," the determined Fawcett - supported by his devoted wife, son and aide de camp returns time and again to his beloved jungle in an attempt to prove his case, culminating in his mysterious disappearance in 1925.
and Option 2
Guardians of the Galaxy 2
What would you choose? Most would gravitate to Guardians simply because they know what to expect, they enjoyed the first one so they know there's a good chance they'll enjoy the second one. They know what genre its' going to be, they know what to expect in terms of story, action, production value etc... The Lost City of Z is an unknown, even reading that plot summary I don't know what the film is going to be about.