JR wrote:This grip adds a lot of grip on top of the disc. Since grip strength puts a limit to power transfer to the disc it also sets the maximum available distance.
I don't think that's true. Pushing down with your thumb likely has very little to do with the distance you can throw a disc, and I believe the primary purpose of the thumb being on top of the grip is simply to help control the angle of the flight plate and thus the disc. I bet you could throw a disc as far with just enough thumb pressure to prevent the disc from "popping up" off your pivot finger(s) as you can with hard thumb pressure. You have to have enough pressure to keep the disc from popping "up" off of your fingers too early and instead ripping out of them, but so long as you achieve that minimum you should be fine and the disc will come off within a very small window of time when you're spiking past your grip delivery pressure threshold.
I'm talking too about people who have a good snap and good pivot, because as I illustrated in my charts about linear-arc delivery lines the pressure spikes quickly. Most people are more rounded and don't have a sudden spike in delivery pressure forces and thus get a mix of slips and grip-locks if they DON'T let the disc "pop up" off their pivot fingers at the right time.
JR wrote:The further toward the center of the disc the thumb is the tighter the forearm muscles get.
The motion of the thumb in that plane is not controlled by muscles in the forearm (the thenar group controls that IIRC). If you lack muscle control then I can see how moving the thumb might activate muscles in your forearm, but that's simply poor muscle control, not a biomechanical fact. PGA Tour pros grip the club quite firmly (though it feels like a 3/10 to them) while retaining loose wrists and forearms. The poor golfer grips too loose with everything or too firm with everything - they haven't mastered the firm GRIP with the relaxed wrist and forearm.
JR wrote:Slowing down the arm pull and making it harder the push the front of the disc down with the thumb.
I do not believe the front of the disc can be "pushed down" with the thumb while the disc still rests on your other finger(s). Your other fingers are against the flight plate and lip/rim. Thumb pressure can stop the disc from popping up off your pivot fingers prematurely (again, controlling the angle of the disc in that manner), but it does not literally push the front or nose of the disc down. If anything, pushing the thumb out towards the center of the disc and applying more downward pressure lowers the back of the disc, not the front of the disc.
So he's simply shifted the pivot point of the disc to his ring finger instead of his index finger. I can see how that would work for someone. He can use the pressure point in the index finger to help him dial in nose angle at delivery and simply have the disc pivot around his middle finger. It makes sense, then, if you're going to prevent the disc from "popping" off your finger (I am making that term up but I prefer it over "slipping" at this moment because it implies an upward move more than one that simply rips out horizontally) that you'd move your thumb towards the center of the disc as it would rotate to be more inline with the middle finger. Your thumb makes an arc, and the farther towards the flight plate the more forward (i.e. towards or in front of the index finger) it can be, and the more towards the center of the disc the farther back it can be.
The problem with player clinics are that players are often the worst instructors because they don't understand that "feel ain't real." I say that a lot on my golf forum but it's true of almost any activity or athletic move. You might FEEL like you're doing something, but oftentimes you're not, so instructors who teach a "feel" as a way of making the mechanics work are going about things bass ackwards - they should be teaching the mechanics properly and determining the feel that produces the best mechanics for that particular student.
We've had students that feel that they have to make 1/2 a backswing with their head moving forward 12 inches just to get their heads to remain still and make a shoulder turn that only goes to 100° instead of 130°.
Players often make lousy instructors. Oftentimes they don't even know HOW they do what they do - they just look out that way and throw the disc and it goes there (and far). Their system of feels is different, their background is different, their faults and fixes are different, and so on.
That said, a clinic tends to cost next to nothing, and even if you can pick up one tiny thing it's often worthwhile, and I'd go to as many as I could within a reasonable radius. Ask pointed questions about how they practice, what their mental routine or outlook is like, etc.