Actually those studies have been done.
UC Berkeley had a very high drop out rate when they were admitting students with low SAT scores. When they increased the minimum SAT for admission, they had fewer black students admitted but most of them graduated.
Colleges do no favors for blacks when they admit them to compete with whites and Asians who are 300 SAT points higher.
There is an excellent book on the topic
https://www.amazon.com/Mismatch-Affirmative-Students-%C2%92s-Universities/dp/0465029965/ref=pd_ybh_a_24?ie=UTF8&psc=1&refRID=TA7Z0B1YQ5Y7D02TSWV0
BRW one of the authors is Stuart Taylor who also authored a book on the Crystal Magnum case at Duke.
Thanks, Lady Jane. Well worth digging into.