So one thing I like to keep in mind is that if a college graduates more people each year, that will mean more alums, but it will also mean more graduates each year trying to work alumni networks to their advantage. This helps explain why, say, small LACs can do so well in per capita placement studies.
So if there was a variable you would want to measure, I don’t think it would be size of the alumni network, it would be the average loyalty/helpfulness of the alums. And I don’t have any reason to believe Penn or Duke alums outscore the other by such a measure.