Great point, and certainly something I'll be on the lookout for.

There is, however, one possible defense in some cases: it could be that the smackdowns in history are the interesting cases and therefore the ones we talk about.

To illustrate using a different set of factors from Diamond, he also lists many factors explaining why Eurasia advanced so much faster than other regions. Maybe the reason we're comparing Eurasia to the rest of the world in the first place, rather than comparing Europe to Asia, North to South, or Old World to New World, is precisely because that was the split where the factors all lined up one way.

(I think this caveat is important to note in theory but actually implausible in the examples given. Especially in Pinker's case: the levels of violence throughout history would be pretty interesting even if they hadn't been in steady decline).