You're missing the point. The fact is kryptonite is something that renders Superman powerless. That's the most important thing. All the things Superman can do, all the things he's capable of... he can't do when he's in the presence of kryptonite.
I'm not missing the point. You made a point that one reason Kryptonite is essential is because it's always been there. I was arguing against that particular point.
It's a storytelling device used to humble the character, pure and simple. It's his weakness. He's a god among men who can do anything he wants and yet he's powerless in the presence of a green rock. It's irony at it's finest. By removing that part of the equation from the mythology, you essentially lose something. It isn't as interesting anymore.
But it's not played for irony. It's never used to make any kind of point or say anything meaningful. It's used as a plot device by writers who don't want to think of an inventive way to challenge the character. It doesn't add anything meaningful to the character because it isn't something real or relatable, it's a plot device. You can accomplish the same thing with something a lot more real and meaningful to the audience, and that's his emotional weakness. A god among men being able to be brought down by a green rock may be irony, but a god among men who's still vulnerable to human emotional weakness is
meaningful irony. A god among men who is burdened by the fact that, even with all of his strength, he can't save everyone or fix everything, that's
compelling irony. And if you throw in other, stronger super powered opponents or supernatural threats, then you have god among men who comes up against threats that are even to large for him to face easily, or even necessarily survive, and that's
exciting irony.
That's what's interesting.
And what's worse, it's an absolute crutch. It causes every conflict to play out the same way: Superman dominates until someone whips out a glowing green rock. It makes the mythology formulaic, and it takes away opportunities to find meaning in the conflict and obstacles in the story. If you find other ways, better ways, more inventive ways of creating a threat for Superman or giving him obstacles he can't easily over come, ways that are rooted in the conflicts and themes of the story, then you get a much more meaningful and engaging conflict.
All in all, all fo the things you describe Kryptonite bringing to the mythology can be accomplished by other, better things that's don't run the risk of deflating the tension and turning the stories into a predictable formula.
I agree with the second part. Bringing Superman to his knees with kryptonite is one thing, bringing him to his knees without having to use kryptonite is far more challenging.
It's also better storytelling.
But that still doesn't justify the use of ignoring one of the basic facets of the character's foundation.
It's not a basic facet of the character's foundation. You can still do great Superman stories without Kryptonite. I mentioned several.
Just because it doesn't show up, it doesn't mean it isn't there.
Actually it does. Not showing up and not being there are synonyms.
The fact is in all of those stories, it's generally accepted that kryptonite is still a "thing" and that it can hurt Superman. Those are stories are already built upon that concept.
Except they're not built upon those concepts. Those stories would be exactly the same wether Kryptnote was ever a thing in the Superman mythos or not. Kingdom Come would play out the same way. All Star Superman would play out the same way. For The Man Who Has Everything would play out the same way. What's So Funny About Truth, Justice, and the American Way? would play out the same way. For All Seasons would play out the same way. That means that Kryptonite
does not matter in those stories. Which suggests, to me, that Kryptonite doesn't matter at all.
The film universe is something entirely different altogether. By ignoring, by not introducing or alluding to it... you're implying it doesn't exist. And I'm sorry, but a Superman universe in which kryptonite doesn't exist... or a universe that exists in which kryptonite isn't an established concept... is sacrilege.
Are you arguing to have Kryptonite because it makes the story better or because it's a thing that's always been there?
I mean, think of all of the other elements of the Superman mythos that were key structural elements of how that mythos functioned that we did away with and we were better off for it. The two person love triangle springs immediately to mind.