I agree with this except for the idea that this is due to a bad translation.
The move to a more dualistic approach with the Devil as a rival is one that predates Christianity (although, as you say, it is ultimately rejected in the Jewish tradition). Reading those ideas back into earlier texts isn't the cause, it is an effect. Like I said, the Hell tradition evolves outside of the Bible texts.
The King James translation choice is reifying a tradition that already exists, it doesn't cause it.
(I don't think we are actually all too far apart here.)