How do you know if an engineer is average vs one of the best?

I haven't heard of anyone who has figured out how to measure an engineer's abilities.

Some people test algorithms. Others test how often they've shipped things. Most just look for years of experience. A few even test whether you know certain facts.

Interviews!

I haven't heard of a single company that has nailed down interviews. I was going to mention interviews but figured that if you couldn't measure how much an employee contributes, you'd have a much harder time measuring how much a prospective employee could contribute given a much shorter time to test them.

"...to find the best and brightest engineers."

Who doesn't say that though? No company says they hire average engineers.

But I agree that their success does kind of prove that they succeeded in that.