Check out Youtube channel lcgm8 for The Stockholm Disc Golf Open 2010 where i managed to film each throw of David to see how often he rounds. He teaches people to not to round and in one interview he said it has given him a profession teaching to pull in a straight line pivoting on the heel. His power comes from timing to a large degree. He does kick forward with the left leg so much so that it moves from back to front left. That counters the backward force of the elbow straightening. You might want to try the Feldy steps because done right it will almost force you to time the late acceleration of the arm well. Dave has variations in how much he bends the arm and often times his arm is nearly straight throughout the throw. Not always though.
Probably the real reason for his distance is the snap.
For more Feldy stuff check out the clinics in Disc GOlf Monthly 94 and 95.
Don't worry it is perfectly normal to not to be able to rectify even one thing immediately. More than two is a crap shoot.

