Many of the evidences for the Book of Mormon would be much easier to explain away if Joseph had written the book in his own time rather than dictating it.
In addition to all the witness accounts which confirmed that Joseph dictated the text, there is evidence from the manuscript itself that
Joseph dictated the book. Most of the errors in the original manuscript are based on the scribe mishearing what Joseph was saying. For example:
Does this leave any doubt that Joseph dictated the book? Why would Joseph choose this difficult method if he was orchestrating a fraud?
See: