They aren't, in the platonic form. But what I think most of us have experienced, in most companies, is that instead of driving compensation and promotion/firin

They aren't, in the platonic form. But what I think most of us have experienced, in most companies, is that instead of driving compensation and promotion/firing the middle-management decisions around those things are made and then post-hoc justified via the performance system. Which is another symptom of HR not having real power and instead simply being used to implement decisions made by other leadership.