[should step away from keyboard....]
To those who think they can get all they need to know from a book, video, whatever, you are probably correct. You will learn enough to be able to safely dive recreational EAN mixes with what you can glean from simple texts/videos. This is truly NOT "rocket surgery."
But what is the purpose of an instructor? Please don't think the instructor's role is to regurgitate the text or such. Should not the instructor's role be to:
a. Confirm the student has, in fact, grasped the information from the materials? and
b. To expand on that information so that the student has a much better grasp of the whys and wherefores of the subject?
I don't know if I'm any good as a teacher/instructor or not -- honestly. I like to think I'm pretty good but, really, who knows? That written, I also spend about 6 hours "teaching" a PADI Nitrox class. I will review, with the students, the questions on the Knowledge Reviews and the Exam to make sure they have an adequate understanding of the subject from the POV of those who wrote the text and created the video. OK, that takes about 60 minutes on average (including the time to take the test). So what do I do the other 5 hours?
We discuss other things:
a. What is most likely to limit your dive -- consumption or deco -- and how to plan/execute based on that;
b. How is Nitrox actually made and what might that affect one's diving and/or gear;
c. Why/when should you use an enriched blend; and
d. How do you actually determine the mixture and then, once you have it, how do you actually plan your dive and do the various calculations?
These discussions take time and, I hope and believe, provide the students with a much broader knowledge base than they received from their materials. It appears that by the end of the course, they actually have a pretty solid understanding of the subject.
But then, they get enough to be safe after the first 30 seconds! But is the goal of the class just to be able to dive safely or to truly expand one's knowledge and understanding of diving and the use of enriched O2 mixes?
YMMV
BTW, my last EAN class had 7 (?) students and was, honestly, very profitable to me!