You’re making all these giant assumptions, and making even bigger conclusions based on them.
It’s only an assumption that language did not come with tool use. There’s no specific language center, so it’s not possible to tell from fossils.
Exceptionally smart chimps can be taught the rudiments of language. I find it hard to believe that early humans didn’t have relatively advanced language skills.
So let's dump language and say calculus. So some caveman from Quest for Fire had a need to work a second derivative to be sure the coal stayed lit, and hence the math center survived 100,000 years until Einstein came along.
Remember, homo sapiens sapiens coexisted with Neanderthals. But homo sapiens sapiens brains could work college math. How was the college math trait something which drove survival and propagation?