Congrats on all the improvements! Backswing looks great. with regards to having trouble with the arms not coming down on the downswing... I've had a lot of trouble with that, recently worked it out. My back swing is very connected with my lead arm angle with the shoulders not becoming more narrow... and at 90* degree turn, I feel like my arms and hands "let go" and the lower body takes over, and my arms fall into position.
Also, as others have noted, the weight seems to be messed up a bit. Your weight looks like it's well on your left side, causing you to tilt away from the target, when the weight should be more even.
Your post 5sk school impact position is near professional like! Good job