I would think that positive learning effects tend to result from high concentrations of top students. Students learn from each other. Class and dorm room discussions presumably tend to be livelier among smart, well-informed, high-energy students. The pace of instruction must be a little faster.
However, all this can happen at relatively obscure colleges. It can happen in the honors colleges, or in the math and linguistics departments, at colleges that overall aren’t too selective (or prestigious). The 10 or 25 most selective colleges don’t corner the markets for excellent teachers. Many colleges enroll more-or-less high concentrations of excellent students. At the top ~40, average SAT M+CR scores are equal to or greater than 1400 and over 75% of students ranked in their HS top 10%. At most of the top ~75, average SAT M+CR scores >= 1300 and over 60% of students ranked in their HS top 10%.
So your smart kid’s alternative to HYPSM needn’t be a community of drooling MBBFs.