Okay, screen cap 1 is telling on a few fronts: so this is the spot in the timing where disc has initiated coming forward from the top of the backswing.
Simon is throwing off the left side of this teepad, but still - same spot in the timing, he's initiated the disc forward - but his shoulders are squared up perpendicular to this trajectory.
Simon, Eagle, most top level guys are going to let the eyes stay with the disc, where you're trying to lead the shoulders with the head.
There's another issue that needs to be addressed: Not only do you need to get onto the frontside earlier, you need to shift so that the back leg tracks forward.
This side-by-side is specifically what I mean when I say "catch and resist the forward momentum". You have to settle onto the front side, with the plant leg angled to resist your forward shift. The by-product of resisting the momentum, is that your backside (trailing leg) is going to shift forward. Look how far forward Simon's back foot has tracked forward between frame 1 and frame 2. That's damn near a foot of tracking forward from the top of the backswing to the disc being at the center chest.
Right now, your back foot is telling me that you're not resisting:
So here we see the byproduct of missing out on the resistance.
1. Angle: the plant leg has to be angled so that you don't blow past.
Hockey players learn this trick early on, when they need to do a "hockey stop" and/or throw a spray of ice at their little sister.
2. Come in with the hips closed. (Simon frame 1) offset /staggered feet for the plant step will make this move easier.
3. Slow down. There is NOTHING about a backhand form fix that improves when you are tryingto do it faster.
I want you to do the following: please humor me on this, I know it's a little wacky... I want you to close your eyes and visualize that you are handed a track and field hammer. I want you to visualize what has to happen in order for you to throw it. Play the internal visualization over and over from multiple angles and watch and feel what your body would need to do in order to accelerate the hammer.
This may take 5-10 minutes to really focus on how you redirect it forward, what direction do you shift to throw the hammer along your line, how do you resist the momentum of the swinging hammer? Where does your weight need to be on your plant leg?
I want you to do the following: please humor me on this, I know it's a little wacky... I want you to close your eyes and visualize that you are handed a track and field hammer. I want you to visualize what has to happen in order for you to throw it. Play the internal visualization over and over from multiple angles and watch and feel what your body would need to do in order to accelerate the hammer.
This may take 5-10 minutes to really focus on how you redirect it forward, what direction do you shift to throw the hammer along your line, how do you resist the momentum of the swinging hammer? Where does your weight need to be on your plant leg?
This type of mental visualization is really helpful when you're making the jump from amateur disc golf swing to high level professional disc golf swing. Not only do you have to drill, throw, fieldwork, video review... but you can benefit greatly by mentally inspecting the broad goals of the motion. What are we ultimately doing? Why do these motions have to happen? What happens when we take multiple systems and link them together?
Lastly, and you'll just have to trust me on this one, if you work on the stuff mentioned above, this will get easier - you are initiating the disc extension well before you've got the disc loaded into the center chest.
And this part is hard, because every bone in our bodies has told us from day ONE that to throw something fast/hard/far - you've got to "put everything you've got into it!" and in disc golf, that's just patently false. You've got to WAIT, stay loose and let the disc and your lower body collect the momentum and then transfer your momentum into the disc, in a very specific place. I call it loading the cannon. Simon shows us exactly where the canon track is: it starts at the center chest with the hand on the outside of the disc and the arm levers swing open, extending forward. That's the most effective track that you can load your momentum into - and if you start "pulling" too soon, you'll likely never end up on the track. You've got to wait and use the body's momentum, not your arm's muscles. By-Product of using your arm: leading shoulder raises up (Your Frame-2). By-Product of using your body's momentum, leading shoulder stays nice and even (Simon's Frame 2) which is a little hard to see in the black jacket.
Using the extension track in the right place is MORE EFFICIENT even moving slowly, than pulling hard with muscles and not getting into the right track.