And it goes on to say "unless such use of copyrighted works unreasonably prejudices the interests of the copyright owner, in light of the nature or purpose of the work or the circumstances of its exploitation in Japan."

Which suggests that when AI art threatens commercial interests, the protection offered by 30-4 can disappear.

To me it sounds like they tried to please everyone and left the hard decisions about conflicting interests to the courts (in particular the courts will have to decide what "unreasonably" means).