Canon Superman beats down Superboy-Prime in a last slugfest without powers, saying that "It's not about where you're from. It's about what you do. It's about action."
The Joker gets his revenge for being left out of the Secret Society by giving Alexander Luthor two shotgun bullets to the head.
Lex Luthor: Oh, Alex. You made a lot of mistakes. You underestimated Superman. Superboy. Me. But the biggest one? You didnít let the Joker play.
What does it say about how dangerous Joker is when Lex Luthor of all people admitted that excluding Joker was a bigger mistake than anyone underestimating himself?
Wonder Woman talking down Batman from shooting Alexander Luthor. It shows not only her character development, but Batman's, choosing to be the better person rather than give into Alex's claims about the universe. He also preserves his morals.
Debatably, Diana underwent no character-development at all; her killing Max Lord was due to the fact that there was no other way to break his mind-control of Superman. With Alexander, there was no pressing need to kill him.
Batman is talked down from killing Alexander Luthor, preserving his morals and proving he's not as evil or broken as Alex thinks. Compare that to Final Crisis, which had a huge YMMV moment when Batman shoots Darkseid.