(1) In the first sentences, the author (a PhD student in history) cannot really hide his irritation that someone with a background in animal physiology has written a popular book about history. I have seen this ad hominem several times about Jared Diamond. Somehow those historians cannot stand that someone with no degree in history has written such a popular book.
(2) "Guns, Germs, and Steel attacked the notion that racial superiority explained Western global pre-eminence, a view taken seriously by almost no one who’s taken seriously"
Actually, what Guns, Germs, and Steel did, was to provide a first comprehensive theory (that I have heard of, anyway) that explains why Europe, and not someone else, rose to dominance. This is the merit. The main merit is not that it, as a side product, discredited the racially based theories.
Failing to understand this difference does not speak highly of the writer of the review.