The amount of bad history from priests and participants of all religions is massive, all of those protesting are hypocrites.
As long as there are no depictions of Muhammad there, then why not tell a historically based screenwriter's fantasy? It's been done since the beginning of film.
Unless the depictions of anyone are "idolising", which would mean no pictures, TV or the Internet for any true believer, which I can't imagine many would do. Islamic medieval geometric art is beautiful, but do people want to go back to that being the only art?
A story is a story, no matter what parts of it are true. It can be an utterly true depiction of history, a fully fantastical depiction of history, or somewhere in the middle, the story is in the storytelling. Its why we have distinctions between myth, legend and history.
I don't think it is possible to make a truly historic movie, 3 hours isn't enough, so this art can't be "historically factual", so it's myth or legend, both of which allow a bit of artistic licence.
I understand why Muslims are affronted by any depictions of Muhammad, but anything that happened afterwards is human, not divine.