[harperlee]

That should not affect the rating by much with an appropriate sorting. See: https://www.evanmiller.org/how-not-to-sort-by-average-rating...

[bjterry]

I would expect people who take advanced courses to rate systematically differently from people who take beginner courses. For comparisons between similar courses it's probably fine, but would be hard to use the scores to compare the value of beginner courses to advanced courses.

Of course, even the definition of better here is so ill-defined it probably is of no practical significance.