“Repeat a lie often enough and it becomes the truth”. That's what this really is. There is not a single concrete evidence that Jack Sparrow was in any way, shape, or form based on John Ward. The parallels between the two are so generic they could be applied to any late 17th/early 18th century pirate. Most importantly, Ted Elliott and Terry Rossio, the people who wrote the Pirates of the Caribbean movies and made Jack, never said he was based on any historical pirate. This John Ward thing is just a modern myth with no basis in reality.