My experience was that it's relatively easy to stack rank Harvard undergraduates, but it often doesn't feel like it serves any educational purpose to do so.

In the class I taught of 12, there were 10 that seemed like they deserved an A or A-. They completed all the assignments and did their absolute best as far as I could tell. Some were definitely better than others (A vs. A-), but giving the hardworking but not genius students Bs just made them stressed out. They would come to office hours to ask how they could improve. The only true answer I could give was "there are 2-3 students in this class that are just incredibly creative and gifted writers, they get the As."

Maybe it's the role of a teacher to stack rank students, but it's no fun. I'd much prefer to try to get the best out of each student. The truly top students are going to have no problem distinguishing themselves later in life anyway, it's just so obvious how good they are.