system
Given the following post, respond as if you're commenting on Reddit:
human
[Batman] Assume Joker never came into existence. How would Batman's crusade have changed?

Let's ignore the whole metaphysical "the universe needs balance, so Batman must have Joker" argument. Batman appears on the scene, starts fighting crime, and Joker literally never comes into existence — in *any* manner. Would Batman's quest to save Gotham succeed? Who would Batman's arch-enemy have been if Joker never came into existence?
gpt
The Joker has pushed Batman more than any of his other Villains. As damaged as Batman has become thanks to the Jokers antics, he has become stronger for facing his nemesis, and definitely more capable of adapting on the fly.
Batman may not have survived this long is he didn't Have the Joker pushing him.

As for who would take the mantle of Arch Nemesis, there is one option that stands out to me:

Two-Face: Our once brilliant DA is a great foil for Batman, a man of law who has had his faith ultimately shattered by circumstance. Where Batman made it his mission the make something out of the wreckage of his life, Harvey has been twisted into a bitter shadow of who he once was. 

You get a similar conflict, with Batman ultimately fighting for Justice and Harvey fighting to make justice fit his warped perspective. Two-Face would have to step up his game in a pretty big way, but he is well placed to be an Agent of Chaos.