Most of these points don't seem central to Diamonds thesis as I interpreted it.

They do negate some of the spurious theories, but the central theory (IMO) is that there's a whole lot of luck involved in global domination, and that luck is not evenly spread.

The one about germs being less of a killer is definitely very interesting though. That's totally central, though -- if not germs doing the killing -- it'd just fall back onto guns. If you happen to dig up the link, I'd love to read through it.