I disagree with this. IQ thresholds exist.

On average, blacks have lower IQs than whites, and whites have lower IQs than Asians. But the difference between black societies and white societies is far greater than the difference between white societies and Asian societies. Because whatever IQ threshold is required for prosperous and functional society, whites obviously meet that threshold.

It's the same thing with understanding difficult and complex information. For example, a median IQ person crosses the threshold of literacy. That's a gigantic hurdle for a lower IQ person, functionally limiting their understanding in ways that are almost immeasurable.