An argument? It's common knowledge, he's a career US underachiever, and some of it is just baffling, losing in straight sets to Murray and Danlil? Nadal and Rog would never lose to a scrub outside of their elite Big 3 memberships in straight sets like that in a final nor allow an outsider like Wawrinka to have an absurd hoodoo over them.
Forget the loss to Kei Nishikori.
The US is just an oddity of a Slam, because there's more to it than just Djokovic's underachievement there. Federer once lost to an unseeded player who might as well have been called the Milkman for all I know, Murray also lost to Kei Nishikori which a big favourite and in the form of his life, and let's not ignore the consistent Serena ranting and raving.