Several points:
(a) not all of the items I listed are found in the KJV.
(b) some of those are found, but were not recognized until well after Smith. Chiasmus is probably the most cited example of this.
(c) there's a wide gulf between simple word substitutions like thee/thou and being able to properly using idioms, especially ones that you don't even consciously know about. I'm fairly fluent in German, having lived 7 years of my life in Germany and Austria, but even though I could easily write a book in English using periodic German vocabulary words properly, I don't think there's any way I could write a book in English that contains dozens of properly-used Germanic idioms.
(d) many people in Joseph Smith's day pointed to these idioms as evidence the book was NOT from God, because of all of the English language errors they created. So it wasn't apparent to those people (who would have had the same background as Smith) that this was "automatically proper scriptural language".