Consider how many books exist on how to care for trees. Each one of them has similar ideas, but the way those ideas are expressed differ. Copyright protects the content of the book; it doesn’t protect the ideas of how to care for trees.
I understand what you're saying but the way you're framing it isn't what I really have a problem with. I still don't agree with the idea that I can't make my own physical copies of Harry Potters books, identical word for word. I think people can choose to buy the physical books from the original publisher because they want to support them or like the idea that it's the "true" physical copy. And I'm going to push back on that a million times less than the concept of things like Moana comic books. But still, it's infringing copyright for me to make Moana comic books in my own home, in private, and never showing them to anyone. And that's ridiculous.
Moana and Moana 2 are both animated movies that have already been made. They're not just figures of one's imagination.
> If I made a Moana comic book, with an entirely original storyline and original art and it was all drawn in my own style and not using 3D assets similar to their movies, that is violating copyright
It might be, or it might not. Copyright protects the creation of derivative works (17 USC 101, 17 USC 103, 17 USC 106), but it's the copyright holder's burden to persuade the court that the allegedly infringing work with the character Moana in it is derivative of their protected work.
Ask yourself the question: what is the value of Moana to you in this hypothetical? What if you used a different name for the character and the character had a different backstory and personality?
> I still don't agree with the idea that I can't make my own physical copies of Harry Potters books
You might think differently if you had sunk thousands of hours into creating a new novel and creative work was your primary form of income.
> But still, it's infringing copyright for me to make Moana comic books in my own home, in private, and never showing them to anyone.
It seems unlikely that Disney is would go after you for that. Kids do it all the time.