If anything, it's exactly the opposite. Performance measurement of developers is an extremely subjective endeavor. One strict objective metric either doesn't

If anything, it's exactly the opposite. Performance measurement of developers is an extremely subjective endeavor. One strict objective metric either doesn't exist or is unfeasible to measure. Maybe your point is to say that "performance is objective but performance metrics are subjective" — sure, I agree. But I'm not sure what that adds.