I didn't notice any legacy admissions when I was there, and only a very small number of students who couldn't hack it and quickly washed out.
(Many students left before graduating, maybe half, but it was only rarely because they couldn't do the work. My good friend had to leave for medical reasons, it was very sad. Another left as a sophomore. 10 years later, he asked if he could come back, and the Institute said "sure", and he graduated with straight A's. I asked him if he'd gotten smarter in the preceding decade, he laughed and said no, it just took him 10 years to get ready to work hard.)
(Many students left before graduating, maybe half, but it was only rarely because they couldn't do the work. My good friend had to leave for medical reasons, it was very sad. Another left as a sophomore. 10 years later, he asked if he could come back, and the Institute said "sure", and he graduated with straight A's. I asked him if he'd gotten smarter in the preceding decade, he laughed and said no, it just took him 10 years to get ready to work hard.)