I think you probably have a different idea about what constitutes success in higher education than the commenter to whom you're replying, and possibly also to admissions officers at prestigious universities.

It can be true that the SAT is a good predictor of university grades, and also that there is more to university life, and life in general, than grades. The parent comment is suggesting that optimizing for grades may not produce the ideal set of university students/graduates. But if you think that graduating with high grades is the whole point of the endeavour then obviously you'll disagree.

Certainly I enjoyed spending my time at university surrounded by people who had more going on than just academic excellence.