I don't think the comic origin of the Joker is really that shallow. I don't think you could call it shallow because we don't have enough information on it.
That's exactly why I call it shallow. There's nothing to it. It's just an event that caused The Joker to become insane and evil. There's no thematic relevance to a chemical bath and what he later becomes, it's just that "mad scientist" vein of storytelling. And I find that shallow and relatively uninteresting in terms of character development and motivation.
"I became evil and insane because I fell into chemicals that made evil and insane".
No one knows exactly how the Joker came to be, we only know he was bleached, and that that event was the "tipping point" for his sanity.
When you say "no one knows exactly", you're clearly ignoring the chemical bath origin which has become canon.
However, we have no idea what happened before that. He could have been abused as a child, beaten, or been a witness to his parents murder. He could have grown up in poverty, lost loved ones, or he simply could have been a man born a sociopath.
He could have been. But you know, I'm pretty sure that if writers wanted us to think this, that this is how The Joker would have been portrayed by now. I submit the following:
What's wrong with the portrayal of a Joker as a completely levelheaded person who was not abused, molested, and did not experience any great trauma, but was simply a man with a particular worldview who became a terrible person through his actions, and made things worse as he went further into becoming that kind of a person.
We have no idea what proceeded the chemical bath.
Depth that "could conceiveably be there" or that could be imagined is not literary depth. So it's still a shallow concept.
I myself like to imagine that multiple things happened to the Joker throughout his life besides his "one bad day" that lead to the breaking of his mental state, and that's the nice thing about that origin. We can speculate because it's never been set in stone. In that way I think the Joker's origin can be very deep.
It could be. But it isn't. Imagining the way something could be does not change what it is.
Now, while I agree that someone who makes himself a freak is also a freak, I think Nolan really missed an opportunity to add to the Joker's character with the Permawhite thing. Nolan has said he wants to make the Joker more mysterious in this one. I think it would add to his mystique if he simply appeared in the movie with bleached skin and it's never fully explained.
I agree wholeheartedly that a permawhite Joker would be more mysterious, simply because he's permawhite. However, it might not be more thematically relevant to the character as Nolan wants to present him. I.E, "The Joker makes himself". Granted, there are ways around that, too, even with permawhite.
You could show how it affects the people in Gotham. Maybe frenzied people begin to say that Joker is more then human like Batman. That he's a monster, some kind of demon that was born looking like a psychotic clown. In my own opinion, I think Nolan missed out on a valuable opportunity to explore the perma-white option more then it's ever been examined, and add another layer to Joker's character.
I can kind of see that. But I would imagine that on any real level, people would care more about what The Joker does than what he looks like.