Oddly, I think one thing in support of your claim is that modern people do better at IQ tests. I've read that if we calibrated correctly, then populations from a few generations ago would have absurdly low median scores -- as if they had actual mental conditions.

But that can't be right measurement. Any test that took a normal person from 1900 at found them to so lacking in intelligence that they can't function in normal life is clearly missing some part of their intelligence. And perhaps that missing something is what you would describe as broad mindedness and robustness.