Dude, I don't hate unnoficial remakes (just the laziness of the Joker film). And the mere fact that Luthor wouldn't end with the "twist mystery" of "was it all false? Debate!" already makes it better than the Joker (actually, American Psycho pulled that off really well, Joker did not).
An American Psycho rip off with Luthor as the protagonist has a lot of potential because of the dynamic between Luthor and Superman. Heck, Superman doesn't even have to appear as anything other than a silent silhouette, but the obsession Luthor would have with being the greatest mortal in a world with a "cowardly arrogant unworthy god" is already a pretty unique thing to bring onto the framework of American Psycho.