Christopher Nolan did the character justice by making him the ultimate trickster. Almost more the personification of chaos than an actual supervillain. More Loki than the MCU's Loki. And the lack of concrete backstory means we never really know where the hell he's coming from.

Now they're going to completely undo all of that.

I didn't care much for Jared Leto's Joker, but I'd prefer that they just ride it out with him over giving us some tragic origin story that's only going to make the character 1000x less menacing.