Wouldn’t alumni networks be a form of prestige effect, although the prestige “ranking” within the group of alumni certainly differs (particularly in greatly elevating the alma mater) from the conventional notions of prestige that USNWR ranking tries to approximate?
Nepotism can be a provider of opportunities rather than results. The beneficiaries of nepotism may still have to earn the results. The difference is that the non-beneficiaries of nepotism may be shut out of the opportunity to earn the results.