To repeat what has been written here and elsewhere
SAT is highly correlated to family income, because of a long list of issues, including, but not only, access to specialized test prep, the ability to have a quiet place to prep, the chances of having a quiet, stress-free place to sleep the night before a test, the ability to take the test multiple times (in Chicagoland’s most affluent school district, kids take the ACT, on average, three times), and access to doctors and therapists who provide the assessments for accommodations (in low income districts, there are around 1.5%, in some of the most affluent schools districts, these reach over 25%).
It is also known that income is one of the strongest predictor for whether a student will drop out of college. So the fact that SAT adds 1% explanatory power to predictions of student success is just as likely to be related to family income than to any innate abilities that a student has.
Moreover, and this is important, college success is not based on standardized tests.
I will repeat this, because it bears repeating: students in college are not passing classes, and are not getting grades, and are not graduating, based on the results of a series of standardized tests.
Success in college requires the skills and competencies that are required for a high GPA in high school. It requires the ability to maintain high levels of quality work over a long period. It requires perseverance and focus to do high quality work repeatedly, over a long period.
THAT is why GPA is a better predictor of college success than any standardized tests.
Furthermore, I am 100% sure that the vast majority of the students with an SAT of 1380 who are accepted to highly selective colleges because (maybe) they applied test-optional will do well in college.
As an aside - income also affects GPA. Kids from higher income families will have the ability to achieve a higher GPA than kids of the same abilities from lower SES families. However, the advantages which allowed higher SES kids to do better in high school than kids from low SES families will likely be carried over into college.
So using GPA is a better predictor, and is likely more equitable, than tests scores, but it is far from being actually equitable. However, that is because low SES kids are more likely to not be prepared for colleges. So to truly make college more equitable, K-12 education has to be more equitable, which is not within the power of colleges admissions people.