For one, you land with your toe pointed to home plate, which means your hips are completely open – thus, you’ve already committed all of the power of your lower half before getting the ball to the “launch” position.
Second, at foot strike, your chin is tilted up, causing your right elbow to be below your shoulder. At this position you will be fighting gravity – throwing uphill – instead of using the benefit of the mound and leverage to your advantage.
That said, try to keep your front toe somewhat closed – just as you would as a hitter – and land with your toes at around a 45-degree angle to home plate. This will keep your hips closed at foot strike. Also, keep your chin tucked down on your front shoulder and concentrate on keeping the shoulders level throughout your motion. Stay tall as long as possible and think about falling down from that tall position. Those two things should start to get your lower half involved in the pitch; as it stands now, based on that one-pitch video, almost all of the force applied to the ball is coming from your arm.