You have a lot of things right in your form. The positioning of your arms/shoulders to drive the discs looks very good. My big critique for you is that it looks like your motion need to get more balanced and athletic. Your back and legs are both pretty straight and you're standing pretty tall when you throw. This means you're not letting the big muscle in your legs and midsection deliver any power. It also means your release is out of balance.
If you look at the first video of Will in slow motion, at about 41-43 seconds his knees are bent, in fact his back knee almost touches the ground. You can tell his legs are flexed throughout the motion and ready to deliver power.
Also, his upper body is bent at the waist and leaning forward towards the ground. It's not exaggerated, but from reach back to release he's probably bent forward at least 20-30 degrees from standing straight up.
Those two things lead to the ideal form to deliver power in baseball, ball golf, disc golf, etc. It's similar to the "athletic stance" that you get in when playing defense in basketball and football, waiting in the field in baseball, waiting for the return in volleyball, etc.
The final thing I noticed in your throw is that your follow through is a little off. But the Beato video does a really good job of explaining that from 3:45-4:45, so just watch and practice that.
To put it all together, the disc golf monthly video from 13:40-21:40 is absolute gold as far as teaching what the lower body is supposed to be doing during the throw. Watch that and practice it over and over as you work on getting more lower body into your throw.