But that gets back to Diamond’s motivating fundamental question.
Why were the Spaniards colonizing the Americas rather than the Incas colonizing Spain?
Why were the Spaniards colonizing the Americas rather than the Incas colonizing Spain?
A more subtle answer is the Spanish commanders had access to thousands of years of military history in the form of books.
The person I am replying to then makes the implicit argument that obviously a poor society would be conquered and then makes the explicit argument that obviously the Incans were poor because alpacas do not count. This line of argumentation relies on the Incans being poor otherwise the implicit argument fails. The implicit argument is being made because otherwise there is no reason to bring up "it's impossible to build a wealthy society" since that would be irrelevant.
I point out how the Incans were not poor and thus their implicit argument fails. I quoted first-hand witnesses who support that the Incans appeared to be quite wealthy and thus the "wealthy conquers abject poor" theory does not adequately explain the Spanish conquest of the Incans.
You are free to make a different root argument, but it is not really the point here. But you do have to make a argument that is consistent with the fact that the Incans seemed pretty darn wealthy even though they were missing certain technologies that we would normally view as critical or indicative of "progress".
It goes beyond the sheer number of soldiers, too - if you have more economic surplus, you can spend it on e.g. things like mining to obtain better materials to make weapons from, on science to construct more advanced weapons etc.
If you do not think that the Incans were materially poorer than the Spanish, the we already agree. If you disagree and actually want to respond to the arguments presented, please present a argument supported by evidence that does not use circular reasoning to demonstrate that the Incans were much poorer than the Spanish.
As an example of circular reasoning: "The Spanish had more advanced weapons demonstrating they invested more economic surplus into weapon technology which proves they had more societal economic surplus." Not to say that superior weapon technology could not be a reason for the successful Spanish conquest, but it is not evidence of a significant "wealth gap" unless you subscribe to the ludicrous notion that all technology gaps are by definition wealth gaps. Even if we did assume that ridiculous notion is true, we have no way of comparing the tech trees of two civilizations to compare their "tech wealth" so it still just ends up being circular reasoning.