These all seem to me to be false dichotomies, which assume that it's impossible either for a single creator to have embroidered their story as they went along, or for multiple creators or editors to have changed the story at different points in time.

According to the messianic prophesies (of which Jesus fulfilled practically none even according to generous interpretations) the messiah was supposed to be born in the land of David, which was Bethlehem. Being from somewhere else was inconvenient for a prospective messiah, so his followers had an incentive to claim that he was from there even if he really wasn't. The hypothesis of a real cult leader whose followers wanted to believe he was the messiah predicts the nonsensical census story better than the hypothesis of an imaginary figure who was invented to be a messiah; much simpler and more convenient to simply say that his family was from Bethlehem.