Do we really need to know, in non-subjective way? In a 1000-person company, how many persons have their performance calculated in a non-subjective and vaguely accurate way?

It must surely only be in sales - where sales volume is a great measure, and I think sales people accept that they are allowed and expected to learn the cut-throat techniques to gameify the situation and win. If we want to force the corresponding personality traits that make such measurement reasonable onto developers - then OK I think story points achieved (aka velocity) is an equivalent measure we can take.

An experienced twisted senior dev would know how to maximise their score there, and make a junior dev look atrocious in comparison, but if its OK for sales then its OK for devs?

(my actual opinion - being subjective and relying on the opinion of good managers is fine. The developer personality matches this.)