I agree with a lot of this.

> My experience of Cambridge students (I live in Cambridge) is that I have seen many burn out.

100%. I "burnt out" (actually, I think I discovered there was more to life than the academic slog I'd spent my entire schooling immersed in) and despite 6 A levels came 94/97 in my third year.

It happens a lot, and my suspicion is that the burnout is caused by the whiplash of going from a high intensity/pressure school environment (where you're likely told you're the smartest person in the room), to a more adult, self-driven one (where it's clear you're not).

> You also end up with a very narrow program of study which for children with broader interests forces them into a box very early.

This depends on the course I think. I did natural sciences which is extremely broad, and allows much later specialisation. Other courses are far narrower d think.