Ivy didn't change for the better. For example, Poison Ivy hates vegans for eating plants. The problem with that line of thinking is that cows are made of grass and corn, so eating a kilo of beef ends up using a lot more plants than a kilo. But Ivy hasn't thought about that fact, because she doesn't have a plan. She's just angry.
Joker, Killer crock, and Penguin kinda had it. Batman the Animated series did a good job reinventing a lot of characters, a prome example is Mr. Freeze.