The Inca still had countless warriors, 80K of them directly with king Atahualpa (though he only had 5,000 unarmed men when he was captured). It took many years of fighting to subdue the Inca despite great providence. It certainly wasn't a boring war.

All the same, I do have some ideas for alternate history regarding disease.

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West Mexican art has been found with large amounts of tin in it, though as I said I'm not sure what the quality was like for a tool. If you make an art object, it's fine for it to have air-bubbles and defects you can smooth away at the surface level, but a tool is liable to break. I wouldn't expect availability to be the problem, since the Americas is one of the most abundant sources of copper on Earth. The Zapotec were well known for their copper deposits, and Mexico became one of the greatest producers of copper later on. Tin was also available.

Apparently, copper and bronze smelting was only coming into its own around the 15th century, just before Europeans arrived. If so, it may be that there just wasn't time to develop a bronze industry. It's also plausible the overly high tin, 23%, in that find may've been intentional, to reduce the necessary temperature.

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Apparently the Tarascan may've used bronze weapons, and even breastplates, against the Aztecs. Also, despite there being no iron forges, apparently some Aztec chiefs had daggers made of meteoric iron: https://www.jstor.org/stable/2844401

So I guess the Tarascan had gotten a healthy bronze age empire going, and were ahead of the others. Perhaps they had factors helping them get ahead.