The knee lift is better than the leg swing for keeping the pitching delivery compact.
There are lots of things to work on with your delivery, but your biggest issue is your arm action in my opinion, so let’s focus on that:
When the hands separate, the throwing hand should go down, back, then up toward the cocked position in a continuous motion along midline while keeping the fingers on top of the ball.
Here are two drills to help develop better arm path/arm action/hand separation:
Separation Drill: Perform slowly! Use 3 lb weights. Slowly mimic the arm action of your pitching motion. Separate hands down and back by squeezing shoulder blades together and thrusting chest outward. Bring dumbbells into “high cock” pitching position. Slowly return to start position. Repeat.
Full Range Of Motion (ROM) Drill: Perform slowly! Use 3 lb weights. Slowly mimic the arm action of pitching motion. Separate hands down and back by squeezing shoulder blades together and thrusting chest outward. Continue the throwing motion right through your follow through position. Then go in reverse. Be slow and deliberate. Use good form. Repeat.
Also, read this article on pitching mechanics I recently wrote and study some of the concepts in it.
Bottom line is if you’re serious about pitching – like really serious – you need to throw, throw, throw. You arm action is a key indication to me that you have a lot of catching up to do.