What was he most wrong about?
> The monomyth is Campbellian imperialism. It's an appropriation of things he despises -- 'dreamlike mumbo jumbo', 'mystic[s]', and 'bizarre Eskimo fairy tale[s]' -- normalising them in an effort to make them tolerable
Jung, who is as associated with dreams as anyone, was one of campbell's greatest influences. Campbell deeply revered dreams, and you could probably find 1000 references of him talking about that's where myths come from.
I think Campbell is the pop version of The Golden Bough. I have only read a little of the The Golden Bough but is so immense, alien and unrelatable. I have also read how James George Frazer was also "wrong". As if the conclusions of a 19th century Victorian somehow negates the 12 volumes of collected mythology. Independent thought and reasoning though is not a strength of those prone to scientism.
I don't know what Jung has to do with anything. But if helps, I also think he was a crank, and the collective unconscious is a neat metaphor and nothing more.