>it tried to explain the shape of history with an overly simplistic model that tossed out every nuance which didn't fit the thesis
I think it's worth quoting Friedman from his essay on positive economics[1]
"In so far as a theory can be said to have "assumptions" at all, and in so far as their "realism" can be judged independently of the validity of predictions, the relation between the significance of a theory and the "realism" of its "assumptions" is almost the opposite of that suggested by the view under criticism. Truly important and significant hypotheses will be found to have "assumptions" that are wildly inaccurate descriptive representations of reality, and, in general, the more significant the theory, the more unrealistic the assumptions (in this sense).12 The reason is simple. A hypothesis is important if it "explains" much by little, that is, if it abstracts the common and crucial elements from the mass of complex and detailed circumstances surrounding the phenomena to be explained and permits valid predictions on the basis of them alone. To be important, therefore, a hypothesis must be descriptively false in its assumptions. it takes account of, and accounts for, none of the many other attendant circumstances, since its very success shows them to be irrelevant for the phenomena to be explained"
Diamond is often criticized for the simplicity, or geographic determinism of his argument but from the standpoint of an empirical science this is a strength. What matters is only the predictive power of a theory, not whether it is nuanced, realistic or representative. People sometimes seem to take almost offense to reductive theories in the social sciences.
Btw one recent development to really test Diamond's theory is I think the development of tropical wheat developed in Brazil. If this works and drastically uplifts the global south I'd count that as a big piece of evidence in his favor.
[1]https://www.wiwiss.fu-berlin.de/fachbereich/bwl/pruefungs-st...