Isn't that the point? Disney counts on having more $$$ and more lawyers than some random artist who might or might not have intruded on the remaining copyrights? So they can bully the artist into submission regardless of whether they are right or not.

The legal metagame around intellectual property has little to do with law as written and much to do with burying your opponent in spurious motions until they run out of money to defend. Odds are good Disney wins that fight against most comers.