En masse such worlds had successes in the past - renaissance, industrial revolution.
It's something else what I can't describe but it's the zeitgeist that was different when world recorded new successes. Look at CS revolution that led to PC and web of nineties and noughties, they didn't think about the result product , or how to steer thousand engineers to build something - amazing things were born in a very small teams, many times authored by a single person, who was deeply invested into the field and knew what he was doing.
Our intelligence has been decrease since the 1970s via the reverse flynn affect. This is only going to exacerbate that decline.
IQ is almost entirely hereditary so "using your brain" has no impact on it unless you're using it for mating.
Do you have a credible source? Average IQ being much lower in poor countries (85-90 in many African countries) is usually explained away as an education problem, rather than being "inferior genes". Of course I understand that this explanation might be more for social/political reasons than scientific ones, because the alternative is racism, but I was still under the impression that nobody knew how much genes vs the environment contribute to IQ. Yet your statement seems quite definitive.