Excellent posts here I think. The fact is that few people are any good at teaching a subject no matter what the knowledge base or enthusiasm. Many superb pilots are useless instructors. It may well be that the below average bloke who has struggled to cope is better than an 'ace' when it comes to getting his subject across. At least he understands the problem.
If teaching were simply a matter of learning a subject and a bit of teaching technique our schools would not be full of hopeless individuals employed as 'teachers'. It is a rare skill where it is found and the demand for instructors will always exceed the pool of people reallly good at it. Hence the logic of the biggest pool possible.