Early humans were not significantly stupider than us modern humans. They were pretty creative in how they solved their problems, and it was their quick thinking that got humanity to the point where we had enough free time to figure out later innovations like bronze, plaster, and agriculture.
A great example of this: They figured out the basic concept of cooking. Apes don't do that, and it allowed humans to eat things that other animals couldn't eat, and meant that humans were far less likely to get sick from what they ate. And while it seems like an obvious thing now, it wasn't at all obvious 125,000 years ago: You first had to get the idea of controlling and later building fires, then the idea of trying to use that fire to make plants you couldn't eat into plants you could eat (perhaps combining them with water), and the idea of heating meat over the fire, and observing that if you cooked your food before eating it you were less likely to get sick.