[woodruffw]

Independent of Jane Street, this is absolutely not true of investment or finance as a whole: there are dozens of large firms where entire management layers are made up of the corporate equivalent of "legacy" admissions.

Finance isn't a purely deductive field: you can't purely compete and reason your way past dumb luck and overwhelming access to liquidity. Institutional players have both, and are more than happy to hire their top performers' mediocre sons and nephews to keep them happy.