Perhaps only that it allows GB to have the bent index because the "bent back" thumb is actually shorter.
A lot of people I see trying to emulate the grip don't or can't bend the index into that "almost" right angle and this is because their thumb won't or can't bend and is too long.
This simply pushes the index finger straight and you get the "pick at the tip of a pair of scissors" look.
Having said that (and suffering from the "PATTOAPOS" syndrome myself too a degree) I don't think that it will stop you from getting the benefits of the tech.
Re the elbow movement and forearm movement. Check out the clip of GB at sound check here in Australia. The lick that begins at 20 sec is the nastiest little lick to play at that speed. I mean NASTY. Please try it. George plays it like he is asleep. No effort whatsoever.
You can see that there is some forearm movement but not much. Possibly the forearm moves because it happens to be attached to his wrist and his wrist is moving. He is also going fast from the top string to the bottom string so the arm has to move a little. I think what we are seeing here is the power and accuracy of the wrist, small movements and pick angle not to mention a supremely gifted player at the top of his game.
Go to 20 secs and work out the lick. Good luck with that!
https://www.youtube.com/watch?v=WACPj-X_TX8