After taking a second look…
One thing that might help is to work on the landing leg calf being vertical at foot plant.
When looking from home plate toward the pitcher, if the landing leg knee is to the left or right of the landing leg ankle, then your lower body has to divert energy / mass to the left or right (away from the target line) to balance the upper half over the lower half. The simple formula of mass=gas tells you that having maximum weight flowing along the target line is better than any alternative amount.
Another thing is perhaps work on some core strength. If he can tone that up then it will also really help to increase the efficiency of energy transfer from the lower to the upper half.
Additionally, it appears (may be the angle) that he lands closed off. It may be an illusion from the camera angle, but it’s something that may help get the hips get more powerfully involved during rotation.
All-in-all some pretty good mechanics.