The idea of measuring individual developer productivity is kind of absurd to me. I'm not saying that what we do is magic, there are just so many variables.
Measuring story points or lines of code is kind of the opposite of productivity. This encourages developers to do as much meaningless work as possible. I'd want a developer to make a task simpler or use an existing tool which means less time writing code. The value of them saving that work from knowing another way is high but hard to measure.
What you want is measuring business outcomes but those are hard to attribute to a particular developer.
I think unfortunately we're left with our subjective judgement here. I think we'd do better admitting to ourselves that we can't measure this than to pretend we have some sort of science here.
Measuring story points or lines of code is kind of the opposite of productivity. This encourages developers to do as much meaningless work as possible. I'd want a developer to make a task simpler or use an existing tool which means less time writing code. The value of them saving that work from knowing another way is high but hard to measure.
What you want is measuring business outcomes but those are hard to attribute to a particular developer.
I think unfortunately we're left with our subjective judgement here. I think we'd do better admitting to ourselves that we can't measure this than to pretend we have some sort of science here.