Former Amazon SDM here. The actual rating process didn't strike me as something all that controversial. I had to do extensive write ups for all of my reports--this was standard stuff: what went well ("superpowers"), what didn't ("growth areas"), and some actionable ideas for improvement.
Then I had to pick numerical scores for "impact" and "potential" that were fed into a black box that resulted in an "overall value" score--this score is meant to be mysterious to the employees but it's the worst kept secret in Amazon at this point. OV ranged from LE (least effort/effective) at the low end, through HV 1,2,3 (high value) which is essentially "meets", and then TT ("top tier") at the high end.
~10-15% of a director org is supposed to be LE, up to 20% TT, and the rest of people distributed through the HV levels. I proposed these ratings to the bigger org that were then agreed to or adjusted by HR and higher management in a formal manager meeting.
The infamous URA quota of ~6% unregretted attrition (PIP) is meant to be met through managing out LE employees. The process starts with a PIP-lite called "Focus" and goes to the real PIP at the next stage, called "Pivot".
Many people got out of Focus, very few get out of Pivot. The part of the process I had trouble with, which contributed to me leaving, is the curve fitting of ratings for people. I had to do things like trade a HV3 down to an HV2 in order to keep an unpopular but otherwise fine performing engineer from getting an LE.
The stories people tell about hire to fire and unfair Pivot are overblown in my experience but not false. From what I've seen, the company will find pliant people and lean on them hard for more and more and more and then manage them out when then start to falter.
Lot of nuance to this--I have no love for Amazon and I'm happy to have moved on. It is definitely a meat grinder. That said articles like this are pretty low effort on my view.