I think that's the thing. Other characters are allowed a chance to be versatile/diverse characters (Look at Aquaman when Peter David writes him vs when Geoff writes him, all done with the mythos of the Flash or Green Lantern for better or worse, the myriad of Spidey, Cap, or Iron Man stories, or Wonder Woman, or even better yet had diverse the Batman franchise has became and the potential to be). Even underutilized, they have been written and handled and depicted in so many different ways from their status quo to their supporting cast to their costumes, they are given a certain amount of freedom as their respective IPs has allowed them to have. It's unfortunate that they are more flexible than what Superman is given. Honestly if given more creative freedom at an earlier stage (arguable post crisis or the 70's or even that boon with Superman Returns came out), I think it would have done a lot of good for the character than what it is now.
Imagine if we got comics like Secret Identity, Space Age, Smashes the Klan, the Earth one trilogy, Birthright, Superman of Smallville, Superman and the Authority, PKJ's Warworld saga, Grant Morrison New 52 origin, American Alien, Superman & Lois during the trinity era. Would the franchise be looked at different than it is today?