detecting AI written code without a minder chained to your arm watching your every movement is still a topic of research...
...and as someone who has been to the last 10 miscellaneous FSF/GNU celebrations I can tell you that community has just as many license cheaters and scoundrels as the rest of the computing world, they just tend to bias towards the good stuff, similarly to how every microsoft employee isn't required to drink the blood of infants (it just looks good on quarterlies.)
If 10 of 20 developers work for corporations and have to pretend that their code is AI written to please the corporations, is that AI productivity?
The advertising and social pressure machinery is so AI heavy right now because most techies are cowards and only speak up on issues (including DEI as we see since Trump) if HR tells them to.
Then of course many projects like Linux or git are entrenched. You can't copy Unix and bitkeeper like Linus did and be immediately successful, because the whole culture is against you (unlike in the 1990s, when the culture was anti-Microsoft).
So yeah, if Gen-Alpha declares OpenAI and Anthropic the new Microsoft and builds up a new counter-culture, then in 10 years you might have some clue.
Otherwise, we have to stick to the current situation and observe that no software has gotten better since AI.