Just one thought, kids at BS don’t typically get through 4 years of math in 5 years, they get through 5 in 5 because the BS offers more advanced classes. I wonder if the issue isn’t clouded by the perception that they are using the repeat year to repeat material. That generally is not the case. It does happen when kids take a course over the summer and repeat it during the school year. I fully agree that regardless, there should be transparency.
And yes, the system favors those with money, whether it’s living in a better public district, paying for tutors, test prep, and enrichment, or enrolling in private school and summer programs. I tend to think adcoms see through that, but that doesn’t mean it’s a good system.