> caveman from 200K years ago would have been just as intelligent as any of us here today, despite not having language

There is evidence to the contrary. Not having language puts your mental faculties in a significant disadvantage. Specifically, left brain athropy. See the critical period hypothesis. Perhaps you mean lacking spoken language rather than having none at all?

https://linguistics.ucla.edu/people/curtiss/1974%20-%20The%2...