With the disclaimer that I've watched the documentary and haven't read the book, the reasoning seemed faulty and unsound to me. It was definitely too deterministic and did not really go into non-environmental factors. For example, it boiled down the state of development of Papua New Guinea civilizations to the primary source of starch being palm trees vs grains, or something to that effect. It feels like picking one contributing factor and focusing on it at the expense of everything else.
I didn't see the documentary, but the book does build a single case, but it's mostly saying "please consider the many, many complex effects of the environment" rather than "don't consider other things."
