I can't agree with this more. The best courses I have taken didn't have a textbook. If I don't struggle at least through some of a course, I'm probably not learning anything. Part of this seems to be that (in my experience) few people are allowed to fail a course. People who both don't understand the material and slack off are just pushed through with the minimum passing grade, dumbing down more advanced courses down the road.
What's old is new again: those who can do, those who can't teach.