I think there will also be other factors beyond merely economics that helped to form this decision.
One of the key reasons for getting rid of the J6/7s is that they need conventional runways for take offs. That not only places a hard cap on maximum launch numbers and rates, it also means they directly compete with manned fighters and high end UCAVs for runway slots. Modern disposable drones will have an insurmountable advantage being able to launch from truck racks and rails, meaning the volume of fire is functionally unlimited, and you also have massively greater flexibility in terms of launch points.
Another factor that may be missed but could potentially be massively important is the PR/moral angle. With J6/7 drones, when they are shot down, as they are almost intended to be, it could provide opfor with combat footage and debris that they can claim as belonging to PLAAF manned jets.
While military experts will be able to easily tell that those are J6/7 drones, it’s basically guaranteed that the western MSM will purposefully ‘misidentify’ them as manned fighters to make it seem like they are doing far better than in reality. Such cheap propaganda points are not just cosmetic in making the PLA look bad, it can also have real impacts on the moral of forces engaged in combat.