It's an interesting question about the balance between qualifications and experience when it comes to teaching. In the end, for sure, you don't have to be formally qualified to teach something well -- but it still helps, right? After all, by definition, being qualified means having had some useful experience. And it *is* important to have plenty of useful background knowledge in a subject. Some of the best-looking teachers are dangerous if they don't really understand the material properly. I'm still seething from an experience where I was volunteering at my old high school, and sat at the back of the class while a teacher went over a class test they did last week. He presented beautifully, really engaging the students well and so on. It's just that, unfortunately, everything he was saying was also total bull.
I did attempt to point this out, but he "thanked" me, and then carried on spouting the same bull, and had stern words with me after about daring to challenge his authority in front of the class. That was fun.
But anyway, he was also qualified as a teacher -- but not as a mathematician, wherein lay the problem. Isolated example? Perhaps. I wouldn't ever want strong academic qualifications to be essential, because I've also experienced the opposite end of the scale (ie superb mathematicians themselves, but also terrible at explaining anything).