Speculation: from a network of opinions and research that, while credentialed and credible, is ultimately motivated by feminism's delight in debunking any kind of dominance other than that of the patriarchy over its victims. I don't mean that the work he used is poor; only that it was preferentially rewarded and promulgated by such a desire.

Anyway, who cares if dominance is overblown in other primates? We can and should study human behavior directly - while some aspects of it may be close to our cousins, different aspects evolve at different rates.