Everyone’s definition of “qualified” is likely to vary a bit. For me, the truest barometer is whether a student will be able to perform the coursework necessary to thrive and graduate from the school.
A significant amount of self-selection occurs during the application process. Practically no students with 2.7 GPA and 18 ACT are applying to T50 universities. Therefore, I think the vast majority of applicants to each university are capable of graduating from those universities. At least 80% of applicants.