I don't profess to be a hitting guru, but I'm studying and learning and ahead of where I was 4 months ago . . . I hope this helps. I'm going to post on this swing on the theory that another pair of eyes may help, even if the vision is only 40-100.
Query whether the swing is too long--e.g., barring. The left arm seems to straighten out too much. Is he maintaining the box enough? (I think no). To me, the straightened left arm is more apparent in the second swing--the one he crushed. My son had same thing at that age--long arm swing can really generate leverage and power, and it often works at that age level, but eventually will need to shorten up to handle better pitching.
Is there an early disconnect (hands drop?)--I think yes. Does he seem to re-connect at/just before contact?--I think maybe, but it's above my pay grade.
Long stride: OK for now, like long arms, but probably shoulld shorten/quicken it as he moves along.
I'm thinking instructor was working on foundation of balance/posture/middle first, and arms/upper body stuff will get tweaked soon . . .
Do you have "before" video?
"Some of my wildest pitches were right down the middle." -Sandy Koufax