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. :-)
There’s one tiny bit of consolation I could offer you, i.e. the fact that the people described in the bom are in good company; it’s becoming increasingly apparent that Charlemagne never existed either. Try doing google searches on ‘charlemagne’, ‘Illig’, and possibly also ‘Heinsohn’....