Once the Book of Mormon was published there was every opportunity for someone to step forward and expose it as a fraud but no-one has ever come forward even as an accomplice. There are no uncovered journal entries, no uncovered confessions. Not even a claim with minimal evidence. Nothing.
This only strengthens the claim that the words came from Joseph.
It would be very different if a credible person came forward to say that they helped Joseph write the Book of Mormon, or any evidence uncovered which shows that somebody else claimed they wrote it, but we don’t see any of this.
If someone else was involved then why did they never come forward? Isn’t the simplest explanation that Joseph, with no notes, and only limited education, was fully responsible?