This scenario has already played out in history when Hernan Cortez took on the entire Aztec empire with only about 40 men. And those were not even modern firearms.
It also happened kinda-sorta when the Chinese sent 300,000 very lightly armed soldiers up against a few thousand Americans in Korea. About 1 out of 5 chinese soldiers had a firearm — they were told “Lee, you run up that hill until you get hit, then you, Chen pickup that rifle and run up the hill until you get hit, then you, RongKai pick it up, etc.” As a result, one of the most common battle wounds in Korea for Americans was the bayonet wound.
40 men plus a lot of natives from other tribes who weren't big fans of the Aztecs taking their members to slice their hearts out to keep the sun rising every day.
In fairness, he made good allies of the peoples the Aztecs were using as human sacrifices.