Well, I believe that effective teaching can also be done through textbooks. Usually, outsourcing study material uses animation which is useful, but, it confuses the students. It is complex in the way of explaining when compared to textbooks. Also, if outsourcing is done, there is no need of practicals and hence students will not gain experience. If practicals are done despite of teaching through outsourcing, then the students will not have curiosity and excitement about the practicals and the experiments they perform. So, a good teaching teaching through textbooks coupled with practicals is very helpful for students that is, they learn better !
In my opinion, textbooks only serve as a guideline on the syllabus and a variety of outsource would make the lesson more interesting and the students have a wider perspective on the topic. Students can also learn more besides what is stated in their textbooks. Outsourcing can also create a more lively and interesting lesson for the class and encourages the students to like the lesson more.