This movie needed a joker with infectious psychotic charisma, absolutely batshit but willing to work with others, play by the rules a little to get what he, and more importantly, Harley, wanted. The original joker didn't play well with others, often it was just him and Harley and maybe a couple of goons, but that joker wouldn't have been able to pull off this kind of prison break. He needed money and influence and power in order to do the majority of the things he did later on pay off debts to get the guard to pass Harley the phone, break into the lab, have enough cronies to break into the lab, and then get to the city to disable Harley. But in this movie, Harley was center stage. Yes, he acted more like a mob boss, looking for power and money instead of just being batshit and dosing everyone on joker gas or fucking around with batman. No, their relationship wasn't good, I wouldn't wish it on my worst enemy, but it was evocative and dramatic so I appreciated it.
The Oscar Wilde quote "I didn't say I liked it, I said it fascinated me, and there is a great difference" really embodies this idea. That literary romance isn't something you would feel comfortable seeing in your everyday life. Someone said that there's a difference between romance in a literary sense and romance in reality, that in literature, "romance" is about writing the id in its simplest most grandiose form, it means "this is beautiful, this is tragic, this is grotesque, this stirs emotion". for every bold daring shitty thing joker did Harley followed it up with her own crazy shit, it's basically the ao3 tag "consensual but not safe or sane". We all know it's bad and psychotic and wrong, but it's also interesting. The other part is the relationship between Harley and the joker.
Part of this is just that the atmosphere of the first movie is a lot darker whereas the second one relied a lot on heavy dramatic cgi gore for its darker moments. These thoughts are a mess too but thats fine, basically I'm trying to get at two things, the first is that I find the first movie more dramatic and compelling.