His counter rotation is minimal, but still present. He could fix that in a few minutes of focused effort.
He goes vertical with his leg lift and with that bit of counter rotation, he’s showing a bit of his back toward home. What you are looking for is to get up and forward simultaneously during the lift and get that pivot leg leaning toward home plate with the hip about a foot closer to home than in the video.
He also gets his arm up early–well before foot strike. He also has a cocked wrist. He should display a more neutral and free wrist position. His wrist position (other than looking very uncomfortable) will limit energy transfer to the ball. I made the fishing pole analogy earlier. He needs to not get that pitching hand up so early so he can effectively fish with a longer pole and get more whip action.
He is also sweeping his leg instead of striding with it. See how his foot is getting closer to the camera as he swings it from right to left in relation to the target line? That action is culminating in a plant that is too open. The hip has to open when the foot does. If that stride can be directly home instead of in a sweeping arc, he should be able to land with his foot pointing toward home and delay his hip rotation for a fraction of a second longer allowing more energy to build before the shoulders start to rotate. This should enhance his hip/separation. He should probably work on a drill that focuses on equal and opposite positioning and a neutral wrist position (hand inline with the forearm and palm facing the same direction his chest is facing.
He does get his elbow ahead of his torso, which is great. His external rotation is not quite 180, but it’s not bad.
Just like McCollum, his trunk is low and is lead knee is too bent. As I mentioned near the top, he needs to get up and forward during his lift. Get that front hip a foot closer to home at the top of the lift. That should position is torso higher and allow that front knee to be straighter. Adding MPH to his fastball from the visual velocity of being a foot closer to home at release due to leading with the hip and another 2-5 mph from improved energy transfer up the body from the braced knee. I’d say his wrist is also restricting his velocity by at least another 2-3 mph.
He could pick up approximately 6 mph of actual velocity on the mechanics and another 3 mph visually.