But the SATs still matter. They are a generalized measure of the student’s quality and are a good measure of how they’ll succeed in general. They should be given more weight than subjective measures. And focusing on them also avoids favoring those “extra” activities that are more accessible to students from wealthy families, who can afford it (money and time). For example, a family that needs the big kid to help watch the little kid can’t afford to have the big kid stay for after school sports.
By the way, plenty of public school students also have good test scores AND the extra things you mention. The big corruption of the process is when these qualified students are displaced by decisions that aren’t meritocratic. That’s legacy admissions but also race or gender based quota based discrimination.