High school grades are gameable, probably moreso than athletic scholarships or standardized tests.

Legacy admissions are part of the hereditary class system. The reason people go to elite schools isn’t just to receive an education, it’s also a status symbol and networking opportunity. If you do manage to get accepted by an elite school purely on merit, that’s not just an opportunity for you personally, it’s a chance to pass that status down to your children.

But yeah the rest of it is bullshit (and often a fig leaf for discrimination).