I'm not a great thrower, but I have done many sports over the years.
He's certainly correct that you cannot think your way through and tweak a throw in real time. It is a chain of events that happen quickly. You have to develop the entire chain of events as a continuous motion. You can break it down in to steps that you work through to reach the end result. Minor tweaks can have significant effects on the outcome.
I don't think this is so different than the "reach back". Just a different perspective. It is all about converting the bodies momentum to disk acceleration and final velocity at release.
One aspect I'm working on understanding is the handle of the whip. When you plant your lead foot, I'm thinking the "handle" extends up through your hips. The whip begins at your torso/abdomen and then runs through your shoulder/arm/elbow/wrist/finger tips.
If you think about the pop of a whip, there is a forward action and a second action in reverse. So, you have the low frequency major wave, followed by a high frequency faster travelling wave. The two waves meet at the tip of the whip causing the snap.
How to duplicate that in the throw?
You "see" it in big throwers in the plant, the rotate and the release. I say "see" it, because it's very fast and i find it challenging to find that micro snap or disc turbo boost at the last fraction of a second prior to release.
Based on all I read/watch, the difference between 300' and 500' is ~20 mph and that 20 mph happens in the last fraction of a second of the throw. The snap. How does one impart that additional force in the last microsecond of a throw? You aren't going to do it cognitively in real time. All the puzzle pieces have to add up to final result.
Sorry for the rambling post. This is something I think about a lot.