While I haven't read the book the author is writing about,  there are some factual errors in this critique that need to be pointed out.

"1) Europeans made natives more violent"

While this statement might have some truth to it in that colonialism pushed native societies into more desperate situations, the idea that "tribes don't immediately imitate the aggressive group and start organizing for war in self-defense, but endure the raids (which happen on average every five or ten years) just so they don't have to" is wishful thinking. Every language I've encountered has a word for "warrior" of some sort, and I've never heard of indigenous peoples, at least in North America, simply enduring violence for philosophical reasons. War was known by "hunter-gatherers", just not on the genocidal scale introduced by European colonialism.

"Plain Indians did not exist prior to European contact. They descended from refugees from other Native groups destroyed by the various European epidemics that wiped out 90% or more of North America's population in the years after 1492, with a new culture assembled around two important European introductions: the re-introduction of the horse as wild herds profligated and filled up the Americas, and guns traded from French fur trappers. The Plains Indians had a post-apocalyptic culture."

This is another hyperbolic statement that isn't really true. There were Plains Indians before Europeans came to the Americas, but their culture obviously lacked the horse. And the inclusion of the horse and gun to their culture post-contact was not evidence of a "post-apocalyptic" culture, but a culture adapting to changing circumstances. 

Overall, there's a general problem of projection going on here, where indigenous peoples, yet again, are used as caricatured architypes for colonial fantasies.