On the concept of a 'historical prophet'
The comments about if Jesus even existed got me wondering about something, while a book does sort of require an entity in it to have existed (assuming it isn't meant as a myth or metaphor) to avoid being disproven out of hand, the existence of such an individual doesn't necessarily mean that the book is true out of hand. Let's try a different example, L. Ron Hubbard existed, we have tax records, birth certificates, etc. that show that he was in fact a real and true person, but that wouldn't make scientology correct , would it? We have fairly good records of the existence of Joseph Smith as well, but that doesn't mean that everyone is suddenly converting to Mormonism. Similarly, let's say that there was an actual Jesus born in Nazareth at the time and place that the bible argues that said JEsus was born. Does that mean that this particular Jesus was in fact the Messiah, does it mean that this particular person performed miracles? Consider various tall tales in American folklore, David Crockett existed, he served in the US government and died at the Alamo, but I highly doubt that he grinned the bark off a tree, rode a rainbow, or any other such thing. We know that certain CEOs, power brokers, etc. exist in the world, some of them we can even walk over and have a nice conversation with but that wouldn't prove that a conspiracy theory involving them is correct.
While I can see the argument to prove that a person claimed to be a prophet did exist being important to avoid disproving a book I do wonder why so many of them think that it would also PROVE that faith and everything in it, even if all the proof that exists is that such an entity existed.