system
Given the following post, respond as if you're commenting on Reddit:
human
[DC] If Batman and Superman had grown up in each other's respective cities, what would happen to Lex and The Joker?

Would they still be villains? Would Lex and Bruce be business partners? Supes could easily handle The Joker, if he had even existed in Supes Gotham timeline.
gpt
When it comes to Lex and Bruce you probably aren't going to see much of a change, Lex would still be largely xenophobic where Superman was concerned and simply changing his geographical base of operation isn't going to change much about what he is. You would probably see a greater rivalry between Bruce and Lex due to their both sharing the same home turf and with Lex being a competent and significant business threat you might actually see Bruce spending less time as the Bat and more visible as Bruce Wayne, CEO.

Now the Joker, true to his name, has always proven himself to be a wild card. If the Joker had been fixated on Superman from the beginning he would have evolved into an opponent to equally match him. Recalling that *chaos* is the Joker's hallmark, his M.O. with Superman would be to keep constantly one step ahead of him and just out of reach rarely engaging in a direct confrontation. He would delight in trying to show Superman that despite his great powers he can't fix everything and quite likely driving Superman down a darker (but not as dark as the Batman) path than he otherwise would have gone.