I think the huge issue at hand here is that I think there is a disparity between everyone because I think there are two questions being asked at once. The first is "Which Superman is the true character?" and "Should this interpretation be the only absolutist version of the character?"
Before I answer these questions, I want to explain that when it comes to art, art pre-20th century used to have more of an authority to it. This extended to most works of art, including literature. There are some notable exceptions, most notably Romeo and Juliet. The Tragedy of Romeus and Juliet, which was a story by Arthur Brooke, was adapted into a play by William Shakespeare, who made it his own and is seen by most as the creator of Romeo and Juliet, not Brooke.
In the 20th Century, especially the latter half, there was a feeling, especially with the rise of photography and more notably film, that made theorists look into authority, and one of the aspects in which art has changed, especially in the 20th century is that more and more works of art were starting to not only lack a single authority (and thus becoming a more collaborative effort), but more and more works of art started to become accessible to all people.
What does this have to with Superman? Well, comics, along with movies and rock and roll, has become one of those 20th century media that has helped change the way we see art do the constant change in authority and reinterpretation. Superman, like other characters has gone through a multitude of changes.
Now which Superman is the true character? If we were going by the old standards of art, it is the original creators, Siegel and Shuster. I am inclined to believe that as I believe that original creator should be true authority on it.
But the new ways of thinking, seeing and interpreting art can answer the second question. Should Siegel and Shuster's original interpretation be the absolutist interpretation? Absolutely not. What we learned about art in the last century is that a character can be reinterpreted and redone many different times, best examined with pop culture James Bond (Not only with movie and novel, but also between authors too), Dracula, etc., that in the era of post-modernism, works of art can be redone to the point that we can have a add (but not remove the original authors) authority to a work of art.
It's the same situation with Shakespeare. He took Brooke's story, added much more to it, and is interpreted as the most popular version of the story. Brooke is still an authority on it, but Shakespeare is now too.
Kurosawa, I do not wish to offend and I'm sure that when new artists and writer are added, they do not wish to offend, but only tell their stories, and thus in turn, tell their interpretation of the character. Batman today is largely different from Superman also, and yet most people believe later interpretations of Bob Kane and Bill Finger's character (the one that doesn't shoot or smoke) as their Batman. Notice I did not say "the Batman", as if we were going by absolutist notions, then Kane's original Batman is the Batman. Still, what is absolute by all means is that Kane and Finger are and will always be the true authorities of Batman, and it is the same with Superman.
And as stated before, Superman has changed before 1986, so the notion that 1937-1986 is the true character is fully opinion, and that's fine. But to say that Superman from 1937-1986 is absolutely the true character as those writers also made changes to Superman's work. Sure there were more expansive changes, but more people have been added to authority before that point in 1986.
I'm not trying to be insulting, and I'm explaining all this in a calming manner, so I wish for the same respect with replies. And this is all opinion just like everyone's posts in here are.
