Ehhh, yes and no. I took it as prescribed every day, but I also had a ton of friends who took it with varying degrees of irresponsibility -- some would pop an XR if they wanted to spend the entire day in the library, and others would literally snort lines in the library at 3 am if they were cramming for an exam. For the latter group, yes, I am inclined to believe they would not hack it in med school, but they all happened to be Econ majors (go figure). For the people who took it once in a while for an extra study-boost, I don't think they were necessarily depending on it to compensate for academic shortcomings -- I think it was more of a lack of discipline thing. To some extent, that's how it started off for me. I was diagnosed with ADHD, OCD, depression; you could probably make an argument that the psychoactive effect it had on me might have mitigated some of the associated symptoms, but I felt like I was being lazy by taking it at first. Not pushing myself to study as hard without it, that is. But after time it became impossible to do without it; it's really addictive. By the end of maybe a year or two I was taking it to be baseline, whether or not I had to study, so I don't think (barring the first semester when I started taking it, developed an eating disorder, and somehow felt academically invincible) it ultimately gave me much of an edge that I wouldn't have had otherwise.
I guess it also depends on the culture of the school you went to. At my undergrad institution (the University of Rochester) it was rampant. STEM majors especially, but I also had friends who were lazy-ass frat boys with BS majors who would take it to finish a paper in a night that they had put off for a week.
