[zozbot234]

> Wouldn't doing a good job earn a good review?

Nope, because incentives are not aligned to that extent. The whole point of a company is that it's not a pure market where incentives are everything by definition; it's a rather more complex organization and these often rely on "soft" constraints as better sources of drive, guidance, cooperation/coordination etc. If you're relying on "hard" incentives (like firing the 'worst' 5% no matter what) you'll invariably distort behaviors in ways that are hard to even predict, and are almost never what you really want.