If you were born in Oppenheimer's era you gained a huge advantage of parents wealthy enough to pay for undergrad school (perhaps a paltry 5%) AND graduate school (perhaps 0.01%) so the gulf in education and knowledge between these wealthy educrats and the average man on the street was far more enormous, and these educrats had a much bigger inside track to discovery ...
So to summarize, a genius is measured by their intellectual height above the AVERAGE person and the average has increased a lot. At the same time, standardized education is killing diversity and creativity...