Earlier quoted context omitted.
Since the effect looks very small, it looks to me like it's only a problem because it adds up if it happens for every assignment for every course. I don't think it needs to average out perfectly; it looks to me like you'd have to be astronomically lucky/unlucky for it to matter if each assignment is in random order.
Some courses are only graded based on a small number of tests. I actually went to UM and a grade might be something like 30% midterm 60% final 10% homework (obviously different professors have different systems). In that case if you get unlucky just twice on the two tests you basically get the full penalty.
Still, yes, you could flip the order from midterm to final instead of randomizing both and the effect goes to more like +/- 0.1 out of 100 for the luckiest and unluckiest.