Our team is getting some awesome shooting distance with just one motor, our shooter design in some way looks like yours. We had some issues regarding the shooting distances so we decided to use the CIM motor without any gears. And we also lifted the tire a little so that contact with the frisbee is made from under the tire (if you want to do this make sure it makes a decent compression). Another way to improve accuracy and shooting distance is eliminating vibration, we are still trying to figure out how to do that, we have already eliminate it to some extent and it has resulted in more accuracy, but we still have some vibration to get rid of.
This is a small (very small)
video of our shooter.
Hope the advice helps you.