The creativity requirements may seem arbitrary but there’s a legal distinction between a sculpture and a standard brick.

What in the world makes you think that?

What is this implication based upon? Where does it say in copyright law that if no copyright arises for your work then it does not infringe the copyright holders' rights? This is completely devoid of logic...

If you record yourself reading a book, you own the audio recording copyright but it would be a copyright violation to reproduce that copy without a license for the underlying rights.

In this situation:

If the AI generates the audio recording of a book, no one owns the copyright of the audio recording but it would still be a copyright violation to reproduce that copy without the underlying rights.

It's like things that are already in public domain. Even if you make coloring book out of paintings in public domain, it doesn't necessarily mean others can just print your book as-is.