There are many films from that era that are still under copyright, because people paid attention to the laws. Disney didn't bother to do that, at least not at first.
We all know the steps the Mouse takes to protect its property, but here are a few examples of them taking the other view.
Bambi: they never paid for the rights before adapting the book. The author's daughter eventually received a small sum after he died, but if the author had money in the late 30s he could have tried to flee Austria when the Nazis came.
Peter Pan: The copyright was donated to a children's hospital. There's a UK law that says that the copyright on Peter Pan will never run out because the money goes to a children's hospital. In the US there is a theory that the Peter Pan copyright was extended at the same time that Mickey Mouse's was. Disney disagrees and is no longer paying that hospital for their Peter Pan things. This link explains
https://en.wikipedia.org/wiki/Peter_and_Wendy#Copyright_statusDisney will crackdown on people legally using things that they claim ownership over, because people cannot afford to fight for their legal rights.
But those "extent the copyright" laws sometimes produce odd legal results. For example, the person who wrote the screenplay for "Nightmare on Elm St" recently reclaimed the copyright for that movie. Any new movie or Freddy merch, well, talk to the new owner. Some of the heirs of Marvel comic artists are suing to get back some Marvel characters (or money to compensate them for those rights).
As for the next ten years - who knows? But it more likely to happen in the USA rather than in the EU. Which will make for interesting times. If things enter the public domain in one country, but not in others, well look at what's happening with Peter Pan.
But the Mouse has learnt that attacking its fans will lead to negative PR. They rarely go after fan art and fan fic, even erotic ones. At least as long as no one is getting rich off them. Filing off the serial numbers (renaming the characters with slightly powers) is more than most fan sites bother to do.
To expand on the Owlman example, he works with the youth of the city. He could be a vigilante busting heads (as Batman does) but instead he focuses on diverting young people from a life of crime. He still battles the super villains because someone has to, but while Batman focuses on stopping muggers Owlman focuses on stopping people from becoming muggers. And Owlet is actually related to Owlman rather than being some random kid Batman brought home. And a few other things, all scrapping away at the "this is a Batman ripoff" and turning it into a "loosely inspired by Batman".
And damn it! I've half written a story when I have more than a score on the go. Yes, I might finish an Owlman story, but the concept is available for anyone else who wants to play with it.