I worked there for 4 years on the AIV / Prime Video platform across a few teams (2012-2016). Obviously we had performance reviews every year, and I did ok. I transferred 3 or 4 times (within AIV), never a problem. I never heard of mandatory quotas to fit in the under-performing category, I didn't hear my colleagues talk about it either, "under-performing" laid off employees were rare (and unsurprising). Was I ignorant of what was going on around me?
From my perspective, the 'bar raising' in Amazon worked through the hiring process, of which I did many interviews. You only hired someone if you thought they were better than average either technically or on leadership principals.
Did this PIP quota thing always go on? Does this go on now to the same effect as people are talking about, or is this an echo chamber magnification of something that happened within a subset of one org?