Is is swing good, he may look decent and be athletically doing the right things to look like a good athlete, but there might be some small things he can do to work on it. It sounds to me like his main issue is driving the ball and making solid hard contact.
I understand this problem as I didn’t drive the ball very well and whiffed a lot, lucky for your son he doesn’t have that swing and miss issue. Now I have worked on a few things and am able to consistently line drive the ball 300+ feet with a metal bat. I am not even 5’7 and may grow to 5’10". Also I have never lifted weights in my life.
On the other hand your son will likely be much bigger than I will ever be. Here’s what I have to share in order from what helped me least to most based on what I was already good at:
- Work on bat speed (but don’t compromise timing)
- Get a decent leg kick or leg slide
- Make sure he rotates a lot during the leg kick to get power
- BUT keep the hands in front of feet during the load/rotation
Just work on a swing that allows him to drive the ball, everyone’s is slightly different.
Since your son is still pretty young you can look at his swing and see if there are and major things he needs to change and fix it. If there isn’t you can choose the swing of a MLB player that is similar to his and ask him to imitate it and see what feels natural.
For me that player was Josh Donaldson.
These videos really helped me: