I think you should be reluctant to generalize from your experiences here. I had the occasional terrible teacher in school (including one who was diagnosed with a brain tumor a couple years later, to the surprise of none of their students), but overall my school experience sounds nothing like yours.

I really, really think you shouldn't generalize from:

I should add that the best loved and respected teachers at the school were all physics, maths and computer science teachers.

The science department in my high school was by far the worst department. I suspect that my experience is more typical because competent people with science degrees have many more higher-pay-and-prestige career options than have competent people with English literature or art degrees.