If the goal were to minimize the number of false positives, I would agree. But the managers of these teams had enough experience to know that they'd rather hire one person a month for a year and only keep one gem than to spend days or weeks trying to find that one gem and then agonize over firing them (knowing that the hiring process is slow and expensive) when the gem loses its shine.

Having done a fair bit of hiring myself, I can't even begin to reliably identify gems. If you know of a way or can explain how multiple rounds of interviews can do a reliable job of identifying them, I'm all ears. I can tell the stinkers right away I think, but gems, no that's really hard. The best candidates I've interviewed (resumes, work experience, knowledge testing, etc.) haven't had any better luck becoming great team members than those with a mediocre interviewing quality.

Cause here's the thing about gems: They only work within their setting and can be created, with some effort and skill, right out of raw material.