2. Slow by who’s definition? It seems like they were doing lots of useful things in a pretty harsh environment. Cleverness for cavemen was measured in surviving and outcompeting other smart humans, hominids and predators. Language and culture got more and more complex and yeah they developed a long list of physical technology.
3. Intelligence isn’t sufficient to produce a lot of technology. For example, domesticating wild grains may require you to be sedentary which itself has other requirements and is something you don’t get when your survival depends on following herds of megafauna around. More than the tech tree often you need some sort of pressure like running out of new places to live and/or running out of the megafauna you’ve always chased.