Occasional underperformance is normal variance as is overperformance. If you can't handle these cases you don't belong in management, and if you fire everyone for underperforming once (your suggestion) you will soon have no workers, and you will cause everyone remaining to underperform.
I think you missed the essence of my comment which was "there is no stack ranking and being evaluated as underperforming is then not a result of stack ranking".
I'm not sure what you mean by `occasional underperformance`? I'm talking about a yearly performance evaluation, in my opinion an overall underperforming for a year is not "occasional", it shows something systemic. The truth is that sometimes we make bad hiring decision (in my group it has been 2-3%). We try to work with them for a few months, set goals, but ultimately you can't always recover everyone.
You haven't defined what you mean by "single occurrence"? To me being low one month, or during a two months project can be a single occurrence, but that wouldn't lead to a "bad perf review" (at least not in my team). Being clearly underperforming for a complete year without changes after setting up intermediate goals for improvements is not a "single occurrence".
When a Sr. Staff which is less productive than other junior engineers, and requires the same level of guidance, something isn't right.
