What would the counterfactual be? The population of elite New England boarding schools, at least in 1934 when the decision was made, was pretty solidly top-1%. (It too has diversified recently because of efforts by those top prep schools to accept diverse applicants on scholarships, but a major applicant criteria they use, particularly for underprivileged applicants, is...get this...the SSAT!). If they're accepting 25% of students from outside the top 20%, that is way better than the situation 100 years ago.