The captain of San Francisco's Fury and the 2013 USA World Games team, Alex Snyder, has a pretty good bio in ultimate. I don't know who is a more accomplished athlete in our sport.
So how does a top level player throw a forehand? If you watch a video or in person, it's all over in 1 second.
This gif will let you see the actual mechanics.
What is happening when Alex throws?
Alex steps forward. A lot. She said that she does this even if the mark is there, throwing past the plane of the marker. Most markers will step back, foul her, or allow her to throw through the gap.
For a lot of players, a big step forward will swing their throw to their left or give it too much outside in - their hips will rotate during the throw. Alex doesn't. She winds up her torso before the throw, and this brings her right shoulder a long way back. It then drives forward in the throwing action, but her hips don't rotate relative to her feet.
Her left arm is out from her body, to counterbalance her throw, and create space from the marker.
Alex has a good range of motion - her right elbow is leading her right hand as she starts her throw. She can lunge forward a good distance. She can twist her torso.
Alex is a good example to learn from.
If you come along to a RiseUp clinic in Australia this week, you'll learn many other things from Alex too. She knows how to coach, and is here to share her knowledge of training for ultimate.