I usually keep quiet on the subject of standardized testing and whether it should be part of the admissions process. Obviously, I have a self-serving bias. But my bias also stems from rational analysis.
The SAT was created in order to make the college admissions process fairer. Prior to the SAT, elite colleges only accepted white, Christian men from wealthy families, most of whom attended elite private schools. That fact alone makes the populist notion of the SAT being for the elite turned on its head.
If the SAT is removed, then how will colleges make objective judgments related to students? The only other “number” involved in college admissions is GPA. The combination of (1) enormous difference between students living in different parts of the country (huge), different parts of a state (big) and different high schools even if in adjacent towns (can be big) (2) varied grade inflation at different high schools throughout the country and (3) the strange bad/good luck of having the tough/easy grading teacher for the exact same course. (I have clients in a local Connecticut school who have the either the easy or the tough grading AP History teacher) makes grades far less objective than a test that everyone can take. That’s not to say that the test should be more important, just that it is more objective.
As for activities, essays, recommendations and other subjective factors… unless you have sat in on admissions decisions, which I have, you have no idea how varied such analysis can be. Human nature is what it is – admissions officials who were musicians tend to like musicians etc. – and makes all such evaluations inherently biased.