* Take about 2/5 of students from the elites
* Take about 3/5 of students who are brilliant
Students of the elites look smart by association. Students who are brilliant are brought into powerful, moneyed social networks. It works well for everyone involved.
The focus on alumni donations is a little bit overblown. Harvard has way more money than it needs. What Harvard looks for is a lot richer than that. The alumni base is part of the national -- and increasingly international -- power structure. A president of some country, a high court justice, or similar sorts of power positions can be at least as important as a billionaire. Likewise, branding is important. The current push on DEI is to make sure that (1) the brand doesn't suffer (2) DEI-focused positions are filled by elite school alumni, and not focused on actual change to power structures.
(Though obviously not in this case because you correctly called it out)
Ivy League this year will have material overrepresentation of Latino and Black kids, substantial overrepresentation of Asian and Jewish kids, and up to 10% 'Children of Alumni', another overrepresentation.
Which leaves those not in those groups out in the lurch.
And one’s ability to pass the SAT proves only that one can pass the SAT. It just proves they were privileged enough to have some one teach them “the tricks and tactics to pass the test” - not understanding, not potential, and not intelligence.