A couple things:

1/ Managers particularly for SDE roles don’t usually have >10-12 people. In reality the URA (Unregretted Attrition) goal is mostly managed at the L8+ level where organization sizes are usually hundreds. Far more likely you have some underperformers in an overall organization of 300, even if an individual team is all awesome.

2/ Interviews at Amazon involve a Bar Raiser who almost certainly won’t work in the Hiring Managers span of control, and the debrief attempts to answer “Is this a bar raising hire?”, meaning is this applicant better than 50% of people in the role/level.

I can really only speak for AWS and Engineering roles, but I never saw any “Hire to Fire” behavior at Amazon, and most every Bar Raiser that I saw took the role seriously and was not a “rubber stamper”.

I keep hearing this trope but this is very naive. A manager simply cannot keep hiring into bottom 6% role. All candidates are subject to the same type of interviews. Every interviewer has to give a "hire" decision for the new candidate. Then there is a bar-raiser interview in Amazon where the interviewer belongs to an unrelated team. They need to give a "hire" decision too. Unless all of this happens, a manager cannot simply hire a new candidate. There is no way a manager can simply hire into the bottom 6% role to keep their good people.