@2017 Lefty Dad, I would advise you not to stay caught up in analyzing your son’s swing by yourself. Even if you can figure out the parts that need improvement I highly doubt that you can properly communicate the fix to your son. The best thing you can do is get video from the perspective of the opposite batter’s box and send it to the best hitting instructor you can find to work with your son. It’s a rare thing for a Dad to be able to coach his own son effectively once they reach HS age. I’m a baseball lifer and I’m one of the few that’s qualified to do it and I didn’t try. I didn’t want the strain of doing that to affect my relationship with my boys. Besides, I’m a pitching guy. And while I understand a lot about the swing I’m not a hitting instructor. I can recognize flaws but I don’t know how to teach the fix. So with my youngest son I got him with the best hitting instructor in our area and the results were fantastic. I learned enough to talk with my son about it but he understood his swing much better than I ever did. And that’s what you want.
This is sound advice, every bit of it. I spent too much time "tweeking" my youngest son. I learned the hard way. He is now with an excellent hitting coach who makes sure he understands his swing and that my son recognizes when he does it right and when something goes wrong and why,, and it is making a big difference.
I do think you are thinking the right way in using the metrics to see if they point out something, rather than just trying to increase or improve them. I do think the sequence is something to address but that certainly shouldn't overhaul his swing.
It might just be as simple as a thought process that keys HIPS, as the first thought after the weight shift happens to front heel strike. Or keeping everything loose but tighten the hips as that tends to activate what is tight fire first. he might be tight in the shoulders and that's making the torso fire first, be loose don't "muscle up".
From some of the stuff you posted, sounds like he isn't struggling and has a good approach. Trust with continued growth of size and strength those one hoppers in the gap will be home runs.