Does it Change Anything if Arthur Fleck isn't the Real Joker?

Considering the possibility, or even likelihood, that we are not supposed to take Arthur Fleck as the "real" Joker, it seems natural to ask what that means for the 2019 film--especially if we take it as a Joker origin story, and find it wanting that way, as I admittedly did. Indeed, I saw in the gap between Fleck and what we would expect of the Joker a failure of imagination on the part of the film's makers in their making Fleck such a pathetic figure; in their apparent inability to imagine that a marginalized, ill-treated working-class man might nonetheless be a figure of intelligence and force, rather than just a "clown" who because of his own inherent personal limitations and nothing else failed to make something of his life the way the stupid and repugnant patrician Thomas Wayne makes out the discontented working class to be.

Thinking of Fleck as other than the Joker we knew renders that criticism moot (if Fleck isn't the Joker anyway then it doesn't matter if he doesn't convince us as the Joker)--but it still seems to me plausible that the makers of the movie, reflecting the prejudices of our time, could not imagine anyone living the way Fleck did as anything but a "born loser," in line with the prevailing tendency to dismiss those who have not "got on" as undeserving of success, and by the same token, as equally undeserving of interest or sympathy from anyone else, all as challenge to this attitude is rarer than before. After all, in the early twentieth century the idea that the American Dream as epitomized by Horatio Alger is a cruel lie was one of the great themes of literature, producing figures from Jay Gatsby to Clyde Griffiths to Willy Loman. What compares with that today?

Apparently not Joker's Arthur Fleck.