But the AI has the work to derive from already. I just went to Gemini and said "make me a picture of a cartoon plumber for a game design". Based on your logic the image it made me of a tubby character with a red cap, blue dungarees, red top and a big bushy mustache is not a derivative work...

(interestingly asking it to make him some friends it gave me more 'original' ideas, but asking it to give him a brother and I can hear the big N's lawyers writing a letter already...)