Because this proves that the “AI”, at some level, is storing the data of the Joker movie

I don't think that's a justified conclusion.

If I watched a movie, and you asked me to reproduce a simple scene from it, then I could do that if I remembered the character design, angle, framing, etc. None of this would require storing the image, only remembering the visual meaning of it and how to represent that with the tools at my disposal.

If I reproduced it that closely (or even not-nearly-that-closely), then yes, my work would be considered a copyright violation. I would not be able to publish and profit off of it. But that's on me, not on whoever made the tools I used. The violation is in the result, not the tools.

The problem with these claims is that they are shifting the responsibility for copyright violation off of the people creating the art, and onto the people making the tools used to create the art. I could make the same image in Photoshop; are they going after Adobe, too? Of course not. You can make copyright-violating work in any medium, with any tools. Midjourney is a tool with enough flexibility to create almost any image you can imagine, just like Photoshop.

Does it really matter if it takes a few minutes instead of hours?