Uhh.. no. I don't know if you ever hired or fired anyone, but, in US at least, if you don't want your unemployment insurance to go up, you want to be able to prove that it was a firing for cause. Perversely, in Amazon case what this means that manager has to hire an employee just bad enough that the 'for cause' firing will be ready for him and he/she just needs to document it.

I fail to understand how people do not see how this simple metric can be gamed. Am I the only person thinking in those weird terms imposed by the system?

My understanding is that even once the manager has filled their team with top performers they'll keep hiring every year for the sole purpose of firing them later in order to meet the quota