A prophet by definition was getting information directly from God and the idea of having to revise info direct from God involves some kind of a breakdown in logic.
Worse, there is every reason to believe that the last real prophet died some time prior to Alexander. The first paragraph of the book of Romans notes that God had spoken to Jewish ancestors in times long distant (to the author of the book of Romans) but that in these later times (the age of Christ) God had sent his son directly to commune with humankind and that supports Julian Jaynes' claim that all such artifacts of the ancient paradigm for the human mind had passed out of existence somewhere around the time of Zechariah.
Precisely!
Joseph was given the ability to translate the BofM. You are ignoring the transmission errors from Joseph to his scribes and from the scribe's copy to the printer's copy and what actually got typeset. No doubt traditional christianity has different notions about prophets and scripture than Mormons. We have first hand experience with prophets and scriptures that you don't. :-)