Always found confident rest for Discus was finger tips, off front finger. A much cleaner release.
Rotational movement should produce a longer throw. However too much rotation at
delivery will detract distance. The Glide movement allows more chances to use the leg and body power and strength and apply more direct power to the throw. The secret is being able to have the right ratio of turn and forward power. I have simplified my thoughts. The whole movement is more complex.