How long ago was that if you don't mind me asking? I was in college 2014-2016, and GroupMe existed but was on its way out. I asked our college interns around 2022 what people use for class groups, and I think they weren't sure what I even meant, but the answer wasn't Discord.
2019-23.
It's worth noting that GroupMe sticking around was honestly probably a byproduct of my own circles and the specific campus culture to a certain extent.