This isn't true. The concept of Batman as it existed in the comics that are in the public domain is open to being remixed and put into new stories and derivative works. Even with the name "Batman" and even without giving any credit to DC comics whatsoever.
What the Batman trademarks are able to prevent is someone trying to use the Batman name to confuse consumers into thinking some product is being sold by DC comics.
As the article points out, the exact borders of what trademark can be used for in terms of merch is fuzzy, but a specific strategy that doesn't work is using a trademarked name to prevent creation of copies or derivative works of something in the public domain
When creating new works with Batman, you'll have to fastidiously avoid using any elements of the character that were introduced later, but you should be good.
Everything in your comments makes sense except this part. If this goes as currently planned Batman will be in the public domain, but not e.g. Batwoman (introduced decades later).
However, I can make my own new superhero now called Foobarman and introduce a Foobarwoman without anyone having grounds for saying I'm ripping off Batman.
So if Batman is in the public domain I'll be able to have a Batwoman. Having a female version of a character isn't per-se a copyright violation just because that path's been taken before.
Of course if I go further and actually rip off entire stories involving Batwoman I'll be in trouble.
I think you're making a legal argument, and I have no idea if your interpretation is what the court has already decided/will decide.
Trademarks very explicitly do not protect concepts or ideas like you claim. Trademark only grants a monopoly on some limited and well-defined identifying design, such as a logo or brand name.
https://www.uspto.gov/trademarks-getting-started/trademark-b...
What Is a Trademark or Service Mark and How Do They Differ From Patents and Copyrights?
A trademark is a brand name. A trademark or service mark includes any word, name, symbol, device, or any combination, used or intended to be used to identify and distinguish the goods/services of one seller or provider from those of others, and to indicate the source of the goods/services.
Sounds awesome.