The way to stratify is med school/clinical performance and interview. All clinical exams should be NBME and these should be reported alongside clerkship evals/grades.
Because if that's the case, then neurosurgery would only be available to those born and bred to attend med school and no one else. Just because someone attended certain schools for high school, college, and med school doesn't mean they're necessarily more qualified to be a ___ than those who went to a different high school, college, and med school. This would be the worst way to stratify.