While The Killing Joke or the Joker graphic novel are more obvious points of comparison given their timely alignment and shared effort to encapsulate what a descent into madness looks and feels like, holding the Joker movie up against Arkham Asylum isn't an unfair exercise.
Arkham Asylum, by comparison, bites into you from the very first page and never loosens its grip until the end.
However, the film, whether it's because of cuts or a desire to build empathy (or both) is unfortunately more toothless than one might want. Being the unreliable narrator that he is, spending an extended period of time in Joker's sole company is a hard task - one that Phillips and Joaquin Phoenix do a decent job of, all things considered.