Well, your elbow is open during the entire swing, then when it's time to release the ball, everything has to rotate... wrist and elbow. Glad it's not hurting your arm... I have to think that it may at some point down the road.
When you open up that far with your entire arm, there are a lot more moving parts. You CAN come straight through the ball with that swing at the release point, it would be a matter of limiting the rotation of the arm/wrist at the bottom of the swing. But, being that there is so much movement/rotation in that swing anyway because of the extreme open position, it's going to very hard to stop the rotation of your arm/wrist at the precise time. It's not so much that your arm is trying to catch up, it's that there is momentum involved from the ball coming down, and the fact that your entire arm is rotating around it. (I would think that the only reason to open up like that would be if you wanted a lot of side roll). Try it standing still with the ball hanging on your arm. Open up your arm, and once the ball comes down, and your start coming around with the elbow and wrist, you should feel that your arm just wants to continue with that motion. I doubt that any human arm could be strong enough, or have the timing to stop that rotation with the fingers at 6:00 every time.
If you want options for the release, I think you will need to straighten out that swing. Like I said, if you want to do that, it may be like starting over... muscle memory is a bear to change... but it can be done.
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