[thisnamedoesntfi]

Forget about what you are doing wrong, you look like you have a good amount of power there, and your armswing is very good. You really need to practice hitting balls off your knees. Tee up a six iron on the range and practice hitting shots off your knees, the ball will hook a bit due to the lie angle of the club. The swing will feel really flat to you. Swing the club behind you then hit in front of you.

Another thing you could do is to hit balls with your left foot on top of a range bucket.

Both of these drills will help you feel what you need to feel to hit the ball consistently. Looking at your swing what you primarily need is better balance.