On engineering career progression at Google: https://mtlynch.io/why-i-quit-google/ … This is the best public description of an important process at Big Daddy G that I've seen. It tracks with what I've heard in less public conversations.
I heard from multiple people that the first pass resulted in what would've been "too many" promos, so the process was re-calibrated to prevent the "excess" promos from going through. It's possible the result is a better process, but it's hard to believe that it's not political.