Novble, absolutely. i was trying to think of how to explain that.
The subject I struggled most to teach initially (at primary) was always the one I had ridiculously high qualifications in.
The ones I really can't do particularly well personally - like art, for example - I teach much, much better, because I found it much easier to break them down in a way that was easy for children to understand, because I knew EXACTLY what might be hard.
Teaching is not straight 'knowledge transmission' - if it was, the subject i was most knowledgeable about, which I understood the best and in the most depth, would have been the one that i taught the best from the off. As it was hard for me to break down, to see the difficulties, to see what 'needed to be taught', I actually taught it rather badly in my first couple of years.
So after a certain point, 'extra' knowledge in a teacher is less important than 'ability to teach'