Intellectual property is imaginary and making a copy of something isn’t stealing it. In contrast, Disney actually has contributed to something which could more easily be likened to theft - namely, strangling of the public domain (after helping itself generously to public domain stories and characters).

I don’t like Midjourney as it’s a proprietary service-as-a-software-substitute, but Disney actually is the greater evil here. It’s probably worth noting that Disney didn’t actually create the vast majority of characters at issue here.