Curves can also hide bad teaching if the students who have the best scores - in a class where there is no mastery of the material - get As. I have always wondered why, even in a hard class, nobody is concerned when the top grade is a 71%. Either something was wrong with the teaching or something was wrong with the assessment, but the root cause is the same. Personally, I would hope that every teacher’s goal is for all the students to knock it out of the park.