But taken as a whole I cannot help but conclude that the program is meant to instil a culture of fear (and by extension toxicity). Considering the following:
* A manager may or may not have made vague statements to indicate you are on this list. Since the manager is explicitly instructed not to talk about the list itself, it is up to the employee to triangulate from a manager's statements their standing relative to performance. This means that employees can never really be sure about their status with respect to this list and so must constantly be on their toes (especially regarding statements from their managers).
* If a person is borderline under-performing, what is the logic in preventing them from switching teams internally? Perhaps a culture change or a product change would tip the scales for them to increase performance. Maybe there is a culture clash with the org or with the direct manager. I don't see any downside in maintaining the FOCUS status but allowing the employee to explore options to improve their productivity internally.
* If a person is borderline under-performing, what is the rationale behind blacklisting them from ever becoming rehired at the company? This the most egregious offence to me regarding the entire program - that Amazon is hanging a sword of damocles over all their employees heads, implicitly threatening them with blacklisting them as one of the largest tech employers in the industry. This list, again, being entirely secretive and Amazon explicitly instructing managers not to talk about with employees.
From my understanding, you can work at Amazon several years, be on a FOCUS/devlist for a huge amount of that time - and never even know. When you leave, you are automatically marked as URA and ineligible to rejoin the company.
This all adds up to me as a program specifically designed to be vaguely threatening and fear inducing.
If we assume an ideal world where managers are all great communicators and can handle performance management with skill and would never misuse the program for any reason - I can maybe squint and suspend my disbelief enough to see how this program can effectively work.
But you would have to be breathlessly naive to assume that's how the program would practically work in the real world with actual managers (and the state of middle/upper management in tech companies at large).
Any management/leadership team who is OK with rolling such a program out at scale given the above is not a team I would want to work with in any capacity, and IMO it just speaks to the dehumanizing nature of the culture they are aiming to create. It is inconceivable that upper management at Amazon doesn't realize these effects of the program.
Like you say, they have probably thought about it deeply, and just don't care. The metrics are working for them, so it continues. I personally am not going to lose sleep over it, I will simply refuse to work there. I hope employees who do work there know that there are other technology companies who actually consider these negative effects on their own employees and actually have empathy towards creating a place where people genuinely want to work - because for other companies, the equation regarding optimizing business metrics lands a bit differently when it comes to their own employees. If you can pass the bar at Amazon you can pass the bar at other places. Don't sell yourself short thinking this is normal or OK.