Imagine if Star Wars was called “Luke Skywalker”.
Even that would have been a little better since it’s a unique name that clearly identifies the movie as sci-fi/fantasy of some sort. But a generic name like John Carter doesn’t communicate any useful information about the movie at all. If you’re going to use a proper name for a title that isn’t a well-known character, it needs to be a unique, fictional-sounding name like Forrest Gump. For a movie like this or Star Wars, though, a single name diminishes the movie no matter what because these are movies about whole worlds and large casts of characters, not just one man’s biography.
Or even better, "Darth Vader"...
the infowarrior