>...it is brutally obvious that a Ph.D chemical engineer with thirty years experience in industry can do a better job...
Brutally obvious until you actually try it. What many people forget is that teaching, at any level, requires a lot more than just knowledge of the subject. If you can't effectively control and communicate with a class, then you might as well go back to your six-figure engineering job because you're a failure as a teacher.
<anecdote>
When I was still at school, our chemistry teacher transferred to another school half way through the year. His replacement was a man who had been a chemical engineer for twenty-five years, and then decided to go into teaching as a change of pace. After two weeks, we ran out of patience with his utter fucking ineptitude in the face of looming exams and put a petition round the class to get us another teacher. Everyone signed, and he was gone a week later to be replaced by a girl fresh out of university who could actually TEACH. We did great on the exams, and she stayed with us for the next two years, and everything was sweet. And she was SO FUCKING HOT oh my god seriously you should have seen her.
</anecdote>
Clearly knowledge of the subject you are teaching, in excess of the syllabus, is essential, but it's meaningless unless you are talented or trained in communicating with the kids.