No one takes Shakespeare’s “History” plays as serious history. Alexandre Dumas’ butchery of history was well known. Nobody ever claimed he was writing history, either. As for the use of cultural anachronism, it may seem artsy to pretentious morons, but to most people it’s just annoying.
A film like this (or something like ‘Lawrence of Arabia’ for example) should be taken in the same light as Shakespeare’s history plays. There are also anachronisms in Shakespeare that both he and his audience were well aware of. ‘Meet Me in St Louis’ is an American classic and goes well beyond the pretentious moron demographic.