I agree with Sultan about the bat drag. The problem with drag is that you lose some of the explosive power that your lower half and torso are bringing to the party. The arms out away from the shoulders are allowing a disconnect from the powerful rotation of the shoulders, hence the drag. Not a perfect analogy, but since you're in Alaska it makes me think about chopping wood. You don't extend your hands out away from your body when chopping wood. For maximum ax head speed you keep your hands in and keep your grip tightly connected to the power of your core.
To correct this you might try a combination of internal and external cues. I'm a big proponent of external cues, but I don't completely dismiss internal cues either. Internal would simply be showing him some slow motion video (e.g. Cabrera, Trout) and note how pro hitters have their right upper arm parallel to the ground when they start to load (elbow pointing at backstop). And their hands are closer to the pitcher than their right elbow (your son's are not). He could try some cues like keeping his bat on his shoulder until loading, but again, internal cues are hard to adopt.
To me, effective external cues are harder to figure out, and vary more from player to player, but in the end they are better at effecting change. The idea is to focus on results, not on technique (let your body figure out the technique). The main issue with drag is bat speed, so measuring his bat speed or exit velocity while training would help. Immediate feedback while he's trying new things will help his body figure out what's working. Another thought is BP with inside pitching faster than he can get around on (just move closer if you can't throw hard/accurate enough). The idea being that it will force his body to figure out how to get the bat head around quicker (by eliminating the drag). I would set the goal as pulling an inside pitch that he can't get to with his current swing.
Just my 2 cents. Good luck.