We recruited the best of the best at grad level world wide.
That gave us a roughly 50-50 American to foreign student ratio
All of our people were far above average
I was responsible for academic integrity and we did not have cheaters
I personally helped shepherd a good number of foreign PhD students through the H1B program for the reasons the H1B program was originally intended for-to give outstanding foreign students with academic credentials and skills otherwise unavailable a path residency and citizenship so they could contribute their unique skill sets to benefit America
That was long enough ago to prove that virtually all of them went on to become American citizens who have made major positive contributions to America
I, most definitely, believe you are clueless on what cheating was actually happening under your nose.
As a student, I saw what you couldn't.