It’s confusing to you because the histories of how these schools accept students is not a linear thing.
No one can predict how the adcoms will accept a student with perfect or average stats.
They would compare you to a “trombone-learning” applicant because USC has a HUGE, well-regarded Marching Band, and if they need a quality trombone player, they will take the musician. This occurred with one of my oboe-playing students (not the best stats but a very strong musician).
I think you need to reconsider why you would want to attend USC because USC does consider what they need for their programs and do compare students. You have to look past your research-based numbers; it’s not strictly numbers. It is very holistic. Stats help, but that doesn’t mean you’re IN. You are basing your admissions chances on what you’ve read, but, in the end, the schools decide, who and what they need.
Also, USC wants a diverse campus and will look beyond numbers and accept students who are artists, athletes, poets, etc. These students may have established themselves with what they bring, and do not necessarily fit the written data you keep alluding to on this page.
If you were to get admitted, how would you pay the $72K per year admission? You can’t borrow that as an undergrad student. The university does have scholarships, especially for National Merit winners, but the scholarships don’t cover everything. It is STILL expensive.