I'd argue that most employers don't really care. They want to use degree, university, and sometimes grades as a first-round filter for screening applicants. Do they actually care if you took the challenging Philosophy course from the good professor, or the easy-A from the Roman History professor? Hell no. So if the primary thing you want is a job, why would you ever take the challenging class? If a professor is significantly and knowingly more challenging than their peers and they don't adequately convey that up front why shouldn't they deserve a bad review. Part of the job is conveying expectations, and in my experience it seems like plenty of professors who will challenge and push know they are like this beforehand but really don't do anything they convey this until after a student is committed.