Jothar, in my experience, most of the students who go off the derech in college are kids who are waiting to be out of Yeshiva and their parents house to do so. (yes, this is just my limited experience) I could have told you who from my high school class wasn’t going to be frum anymore well before they graduated.
BS”D
Of the 10 or so cases of OTD I knew in college (who were by no means compensated for by myself and another handful of BT’s but I had made up my mind to go as I did before I started college anyway and would have dropped out to learn Torah if I could have), 2 were as you described. The others had spent 1-2 years learning in tzioinish yeshivos before college and came in shtark – but left frei or worse yet, CONservative.