I’m ignorant of the geology there, but Wikipedia says copper was available. If you are saying they had unusually easy access to tin, then they sort of had the ability to make bronze without the long-range trade. Is that right?

That would seem to support the theory in a way. If they could make bronze “in their back yard,” the same way that everyone else could make iron in the Iron Age, they would be sort of living in their own proto-iron-age, right? (In the sense that access to metallurgy was democratized). So if anything, it would provide some pretty strong support of the link between democratized metallurgy and more disperse power.