The Joker isn't supposed to have any definitive origin and it's blatantly stated in the Killing Joke that the dead wife origin was false and he always changes it because he doesn't really remember what happened to him, Also the Joker is meant to be a straw nihilist who wants to ruin everything for everyone just to show how stupid it is to care about them, But here the Joker clearly has a motive about being a rebel and becomes V