Agree, lots to work with. That initial step way to the left throws him off "horizontally" or "east-west", IMO. Watch how much his head moves from left to right from the start to finish. You want less head movement and more kinetic energy building with "north - south" movement toward the target. Contrast his head with Gerrit Cole, for example: https://www.youtube.com/watch?v=Mm5A1wAbmE4 .
When I was teaching 12-14 year olds (I am not a coach, just a dad who pitched D1 who pretended to be one for a few years), I did drill where I would stand behind the pitcher and put my hand on his head during the wind up. Just slight pressure to try to help reduce the side to side movement or, at least, make them aware of how much they were moving left to right. You likely can't eliminate it completely, but...well Gerritt Cole nearly has. I think this helps with the ability to repeat the delivery and with command.