Seems like, in the search for distance, your actually got:
- a reverse pivot,
- a downswing initiated by his shoulders.
Sorry I can't advise you any teacher, i'am not from the USA but I think you are actually right in your quest. Find him a pro to get him back on tracks before its too late. I used to think that teachers were not necessary and now that I hit millions of balls with a faulty swing, it is the triple (and more) work to get back to normal.
Good luck,
Eric