The title of the movie takes itself entirely tongue in cheek. This movie is to Ned Kelly like what "Once Upon a Time in Hollywood" is to the Manson story.
Its someone's entirely dreamed up take on the subject (the book it is based on, was classified as fiction). And that is perfectly fine.
Entertaining, good acting, good scenery, does slide a little in the second half. The "C word" is an Aussie staple, so expect it!
I do agree with other comments about Ned needing a beard - it was his second best known trait!