[jfb]

"Also, many of these "disaster" cases may simply be suffering from an unfortunate, but all too human cases of stage fright, especially if it's their first F2F at a big company like Apple."

This is absolutely correct, and there's no hard and fast set of rules to determine if performance in a staged, artificial environment like an interview correlates in any significant way with performance at the job intended. There're a whole host of issues around hiring in particular and coping with humans in general that the tech industry does an astonishingly bad job with.

To me, the goal of interviewing is not to find someone who is a clone of someone who already is on the team, but rather to find someone who brings different and useful perspectives to the job. If they can work on existing problems day one, so much the better, but if they can never get beyond working on existing problems, then they were a mis-hire.