Comment by morsecodist

I don't think it is absurd to reason about individual contributions, just to focus on measuring them with metrics. I have been on the management side as well though I admit I am much more of an IC. But the way I think that should go is laddering up to business value by describing what the person did and why that contribution was important.

So for example I would say something like: X deserves a promotion because their work was important to delivering project A on time. Project A was difficult but worthwhile because it allowed us as a business to meet goals 1 and 2.

That said I mostly work in smaller orgs. I have never been in a situation where a manager would be so removed from a team they would need a sort of proxy metric to direct them where to focus their attention to understand what the people on their team are doing day to day. I can see how this would get more difficult as a company grows.