LoC is a terrible metric for comparing productivity of different developers, even before you get to Goodhart's Law.

OTOH, for a given developer to implement a given feature in a given system, at the end of the day, some amount of code has to be written.

If a particular developer finds that AI lets him write code comparable to what he would have written, in lieu of the code he would have written, but faster than he can do it alone, then looking at lines written might actually be meaningful, just in that context.