How are you going to compare their productivity?

I'm going to look at the total desirability of the what Adam does, at the total desirability of what Bob does...

And in the end I'm going to have to make difficult calls, like how desirable it is for us to have weird chunks of code that look strange by consume noticeably fewer resources.

Each of them is better at different things, so as a manager I need to take that into account; I wouldn't use a carpenter to paint while the painter is doing framing, but I might set things up so that painter helps with the framing and the carpenter assists with the painting. I certainly wouldn't spend a lot of time optimizing to hire only carpenters and tell them to build the entire house.