Totally agree about the instructor not using a camera.Most agencies disallow instructors from carrying cameras, lest they lose focus on their students' safety. I agree with that. A friend or a DM can do this, but they aren't always a part of the class.
I was recently, last Thursday, in mentoring an experience diver getting familiar with the new kit they had bought.
Within 2 minutes I realised I needed to give the individual my full attention, so clipped by camera off. We then spent 15 minutes going through buoyancy drills.
In a club environment most learning is done outside formal lessons. In an instant I went from being a dive buddy to instructor. It didn't mater the student was an assistant instructor, they still needed guidance.