I would say it's kinda grey area, beacuse even human made designs are kind of a mishmash of many ideas that have been there before aswell.
AND AI generated imgaes aren't protected by copyright (see here) and can be used in any way, as far as I know.
Even big advertising agencys are doing that. They generate an image and copy or trace the designs to thier products. Working with AI hand in hand
I think its more a question of your own morality and it's totaly okay not to like that practice!
To be honest, I don't mind if someone takes an AI Design, reworks/redesigns it for thier own purposes. I see it like that: It becomes something new with an AI as a base / rough shape.
Especially with characters. Characters aren't only images or certain designs. There are more parts (like description, personality, story) that makes my character, MY character.
But taking an AI image reupload it 1:1 and claim it as your own? ... nah