I have worked with people from Polytechnique, ENS, INSA, and other schools like Supelec. They are above ordinary people, but this is to be expected; however, most of the people I met are unable to create like Fabrice Bellard did.
I guess something has changed several times in the past, for example, the number of Nobel prizes per inhabitant in France dropped in the first half of the 20th century, and I don't know why.
I also remember reading a text in the 2000' by a Polytechnician who complained about the new generations.
*I have an immense admiration for Fabrice Bellard*, but he is an exception among these school populations.