Regarding trade and spread of ideas in the Americas, I believe later in his book Diamond goes over the fact that if you look at the contents of North and South America, they’re connected via a tiny (relatively speaking) stretch of land, whereas Europe and Asia have vast swaths of land that connect the two. Also, the big things in his theory are lines of latitude being crucial to successful trade. Europe and Asia share lines of latitude, North and South America do not, they share lines of longitude.
The civilizations in the Americas (Inca, Maya, Aztec, etc) certainly were advanced and powerful, but when compared to the Europeans they fell short. The best thing we have in terms of ways to measure the two against one another is what happened when they clashed, and the Europeans dominated that affair. Granted it’s an extremely imperfect comparison, as the Spaniards (and future Europeans) had a biological advantage of using a small group to spread massive epidemics to an enemy continent, but it’s the only one we have.