The validation of fiction through the mindless label of being "based on" actual events is a popular and persistent delusion. Historical drama is saturated with interpretation by writers, directors, cinematographers and performers, and the phrase "based on" typically does a lot of heavy lifting. No aspect of the production is ignored for the purpose of conveying meaning, and what you are consuming is a multitude of artistic interpretation. Of course there's nothing at all wrong with telling a story, but telling a story whilst pretending your story has the imprimatur of documentary is dishonest.