True, but that is not the same as proving someone cheated. Besides, when you have too many students, you cannot talk to all of them one-by-one in any meaningful way. Or assess them in a meaningful way, to be honest.

By the way, where I work, management pushes for stuff like proctoring, and more students, and "measurable" results, and so on. As a teacher, I don't care much about the whole grading show.