I managed at Amazon and Google. One nuance to the Amazon stack ranking is that it is supposed to be only applied at org sizes > 50 or levels > 50. In theory Line managers themselves shouldn't feel too much pressure on their teams to do this. I do agree that it should be an even larger N (e.g. 200) or larger as Google has the same effective policy but their N is much much larger. The scale of the stack ranking really matters for how toxic it can be IMO.