https://en.m.wikipedia.org/wiki/Campbell%27s_law
If you know a thing or two about evolution, it should be obvious how these shortcuts will play out.
And still, you hear about similar metrics being used all the time... All over the place.
I suspect, in most cases, it's actually bad metrics stacked and really the manager trying to putting a metric on their own "contribution". (Parasitic isn't even the word, but rather viral or prionic...)
In the end, truly and reproducibly recognizing individual contribution is probably beyond human comprehension for any non-trivial tasks. Maybe your product actually benefits a lot from that one guy, who is just very good at promoting a good spirit, being fun to work with, rather than being the most proliferative coder. And how do you measure how hard a problem is? Does is matter who perceives it as hard in your team?
I think, it's one of those things, where trying to be clever will most likely make things much worse because the manual labor and personal involvement of the past actually was already best fitted for the task, by utilizing the human brain where it excels. Humans doing human things with humans, without being willfully ignorant about the complexity at hand.