Not gonna change much upstairs intially but bottom half is stiff. Get some flex in the knees and weight back a bit and stick the butt out some.
Really basically a no-stride hitter...might help him you to actually stride.
Understand a stride is not a step forward but a reach with the front foot...weight isn't transferred. Think smooth reach. Front side (stride leg) is collapsing because weight/torso is moving forward; front side isn't firm and there's nothing to hit against. Hip rotation is finished by recoiling back after contact. Hips are sliding forward and not rotating properly. Not getting any real power from the torso. In essence, a linear hitter.
Personally, would like to see a wider stance (4-6")if no-stride is method; that and keep weight back. If you stick no-stride, a higher knee lift will help get weight back somewhat; just don't go to crazy with it. Careful with hips "opening in the stride"...front heel hitting ground intiates hip opening otherwise you will be a sucker for offspeed balls in the lower part of the strike zone.
Way too many hitters get the "stand tall" message with actually standing tall with straight legs.
Strong kid that with a bit of improvement in posture will improve..has decent batspeed already without using his lower body. Good instructor and a few sessions/reps would fix this pretty quick. More good than bad stuff. Hang in there. Takes guts to let faceless people take potshots at your swing without them giving corrective advice in return.
Ever practice hitting a heavy bag? You'll feel what I'm talking about with a front side collapse....the bat stops and you'll feel the front side/leg breaking down. An Army duffle bag filled with rags/newspapers works fine; just hook it to a fence at the field and take some swings. Easy to check body position at impact. Similar to hitting a tire but better for checking impact as there is no recoil.