Yes, but his specific prior probability is "chance of ancient authenticity".Right. If he was trying to convince people that he spoke to God and had the powers he claimed, then we would expect (Bayesian at work here) something like a Biblical fan text, accounts of seeing God and angels
The consistency of his visions or even if his visions are real have nothing to do with the Book of Mormon as ancient. Inspired fiction or twenty other possibilities.
If you expand the project to what he really meant, instead of what he actually put on paper, that in extremely broad terms, is Joseph Smith and his work what he claimed it to be? Okay, once it's established that we're evaluating the components of a cult, then are 8 super loyal followers who toe the party line correlated with a long, rambling manifesto? Yes, I think so.
and yes: turning 5 to 6: change length of document to length of chapter (granting it's relevant when it really isn't).