One problem I have with Diamond’s theory is that I doubt that there is anything for it to explain. The Americas and Eurasia/Africa were essentially isolated from each other for about 15,000 years. In 1500 AD, the Americas were roughly 3500 years less advanced than Eurasia/Africa. That seems well within the random variation one would expect between two isolated instances of human cultural development over a 15,000 year time span. If you think there is still some remaining indication that the Americas were disadvantaged, the fact that the Americas are about half the size of Eurasia/Africa seems like a sufficient explanation.
One problem I have with Diamond’s theory is that I doubt that there is anything for it to explain. The Americas and Eurasia/Africa were essentially isolated from each other for about 15,000 years. In 1500 AD, the Americas were roughly 3500 years less advanced than Eurasia/Africa. That seems well within the random variation one would expect between two isolated instances of human cultural development over a 15,000 year time span. If you think there is still some remaining indication that the Americas were disadvantaged, the fact that the Americas are about half the size of Eurasia/Africa seems like a sufficient explanation.