Superman isn’t 100 yet. Superman first appeared in 1938, and is slated to hit the public domain pretty soon, along with Batman and Wonder Woman.
As for absurdity? One of the bundle of rights in what we call copyright is the power to sell it outright. You can’t sell something devoid of value. (Well, besides NFTs.)
Besides, as pointed out numerous times, Supes has dozens of non-DC knockoffs despite being under copyright…and a fairly valuable and well defended one at that. I find it absurd that people utterly unconnected to the creation of a piece of IP feel a need to assert a right to using the EXACT copyrighted form is something as opposed to an homage after the mere passage of time.
With other forms of property, that doesn’t really happen.
How does using the original IP of something serve the public good when alternate versions are perfectly legal?
Certainly there are differences. But they’re not so great that it somehow justifies the shortening of copyright durations,