Those same universities have selection criteria which predict success after college independent of the college attended. So it's not like they are masterfully teaching anything; rather, it seems very much like they are simply rebranding the best students.
To the extent that they also teach students more and better, this is actually damaging socially because it sucks secondary educational capital into a few locations. Lower end schools could do more and better if they housed many more bright and ambitious students. But if they're all going to a handful of schools, they're not improving the social networks at Random State.
Although elite universities might not "masterfully teach", the students at these universities still learn more than students at a lot of universities simply because the classes are more difficult (these are generalizations, not the rule). If classes are more difficult/cover more content but aren't taught well enough/not all content covered, then highly ambitious students just end up teaching themselves a lot of the curriculum, but they still know the material of their classes by the end. Essentially, even though the teaching might not be better, I believe an average MIT student studying X comes out more knowledgeable than student from [[ state school ]].
And its an interesting thought to distribute top students. Assuming a fixed quantity of "bright and ambitious" students, wouldn't sending more of them to lower end schools weaken the social networks formed at elite schools and destroy something unique about American education system?
To the extent that they also teach students more and better, this is actually damaging socially because it sucks secondary educational capital into a few locations. Lower end schools could do more and better if they housed many more bright and ambitious students. But if they're all going to a handful of schools, they're not improving the social networks at Random State.