This is a fair argument and I will concede that if we're thinking about success as the getting high quality compliance for managerial games (which really does make up most entry level work in finance, consulting and tech) then hiring from a top school is highly predictive.

Going more meta, starting a median VC-backed company in the Valley is largely playing the same kind of game as in elite private schools and colleges - observing a social scene, identifying powerful players and the ladder to reach them, meticulously performing the necessary social roles in order to achieve funding, cargo cult management styles from the group.