Ideas are not ownable.
Copyright is about “the concrete expression of ideas,” not the ideas themselves.
You can’t use them in exactly the same ways that someone else did. But you can use them.
You want to write about a kid who sees his parents murdered and sets out to fight crime? Go right the hell ahead.
[Actually, you can probably do all of that if you make it feel different in keys ways.]
But ideas themselves are not property. They’re free for anyone to use.
But it doesn’t need to be DC-owned. It doesn't need to be _their_ Superman. And I’d be able to do it better without someone else...
If Superman were in the public domain by now (as I think he should be), I’d do it with Superman. Since he isn’t, I’ll do it without Superman and everyone who reads it will know that I’m writing about the idea of Superman.
It’ll be a good story.