Is that Joker really considered as definitive? I've never seen such claims, or very, very marginally.
Seems to me like the consensus is that Phillips and Phoenix are just doing their thing and that it's clear we're dealing with "Arthur" more than "The Joker".
I mean, does anyone really expect this character to end up like the classic "Clown Prince of Crime" and face off against Batman?
One might ask why use the Joker brand if the story is so different, but that's also what made Elseworld.
Personally, I'm fine with it, as I don't care much for comic book dogma when it comes to adapting them for the big screen (as long as the essence is still there).
EDIT: Sorry, I'm parroting the last posts...