If my business depended on a legal fiction to be true and I had invested a whole pile of effort + money into it being so then I would argue at every opportunity that 'of course it is legal'. But that's just a version of fake-it-until-you-make-it and in practice not all of those bets pay off.

The fact that meaningful contribution has not been defined is a strong signal that things are not nearly as clear cut as you make them out to be. Until there is a ruling that clearly establishes that the person that generated the prompt owns the copyright on the code I think it is misleading to suggest that this is already the case, your lawyers are not the lawyers of the parties that will end up hurt if it ends up not being so.

For contrast: we have a very clear idea on what things are copyrighted and in general these things do not rest on a foundation of IP appropriated from others outside of the license terms. The fact that the infringement is fine grained and effectively harms the rights of 1000s or more individuals doesn't change the heart of the matter, whoever wrote the code: it wasn't you.

Given your bias I'm not surprised that this would be your argument though, effectively you have created a copyright laundromat using code that you were nominally the steward of and not the owner but whether it stands long term or not is not up to your lawyers.