I think there is a selection bias here though. My experience is that the people with the best natural teaching ability are not teachers. They end up in random

I think there is a selection bias here though. My experience is that the people with the best natural teaching ability are not teachers. They end up in random industry jobs because dealing the career ladder of teachers is super unappealing. In contrast, the teaching profession is full of people who were good students. So requiring more degrees does not do a good job of separating the wheat from the chafe. In my experience, the best teachers are people in their 50s or 60s who have a ton of diverse experience and still chose to teach. But the median teacher is someone in their 30s who has only ever been a teacher.