That is the conlcusion of this paper by Lant Pritchett & Amanda Beatty. I could not agree more. That also applies to a large extent to economics teaching in college in developed countries (see: Are we teaching too much?)
What is the problem?
Probably the problem is a combination of too ambitious textbooks and equally ambitious professors. The new textbooks cover a lot of material and professors have the expectation that they need to teach all of it (I have in mind micro and macroeconomics textbooks). Young professors are more ambitious than older ones in terms of the material they want to cover.
Experienced professors can teach us one or two things about how much to cover in an undergraduate class. They pick and choose, less experienced ones want to teach everything.
In fact after careful consideration I decided not to use a required textbook for my principles of microeconomics class this semester (this is my recommended one). I will let you know how it goes. Basically I will use a set of handouts that a former professor of mine, Julio Cole, wrote. They cover the fundamental concepts, to the point. I will complement them with a chapter a day from Landsburg's new edition of The Armchair Economist, and we will analyze movies using economic concepts: Hunger Games, The Hobbit, Amistad, The Godfather, Moneyball, and City of God.
Nowadays there are so many resources online, such as videos, podcasts, etc., that using a textbook is less and less important. In fact, in my econ classes at George Mason, we read mostly books, papers, and handouts; rarely textbooks . . . well, we had some, but we did not focus on them (granted, it was grad-school, but still). Even though we did not focus on textbooks there was a lot of fun and learning. I am not saying that textbooks are unnecessary, but probably they are overrated.