“Last year, reports noted that Amazon’s goal is to filter out the bottom 6 percent of employees, and that it didn’t necessarily let employees who were at risk of losing their jobs know so they could actively work on improving their performance.”
This is 100% true, and most years it is 10%. It’s amazing when you have someone in the bottom 10% transferred onto your team in a re-org. The first 1:1 is the employee asking for help getting promoted, because the prior manager was that opaque about the performance issues. I was able to coach up the person, but I was dinged for not “hiring and developing the best.” You’d think that leadership principle would be about coaching people up. No, it’’s really code for purging the bottom and replacing them.
Oh, they also promote management who have active complaints for verbally abusing employees. Then the whole department gets sent to sensitivity training.
There’s an entire marketing team dedicated to convincing former employees to return. I’ve been asked to go back. I honestly couldn’t stop laughing. I’m pretty sure my response got me removed from the list 
My current boss was at Amazon less than a year. We didn’t cross paths there, but that’s how bad his experience was.