It is not elitism. I know several developers from Epitech that are very very good at what they do. However, they can't be compared with graduates from the top grandes écoles, simply because none of these grandes écoles focus as much as Epitech on training developers. It is a broader education. As a result, graduates from grandes écoles can work pretty much everywhere and most of them don't actually work in tech (usually finance, management consulting, etc...). Epitech graduates can't.

Graduates from Epitech, or 42, are very far from having the same ability with mathematics and quantitative sciences in general. That being said, it probably doesn't matter since most tech projects don't require such skills.