Seems your rudder is a bit too sensitive. That is not only aproblem while gunning in buffs. You will also use rudder uninationally while flying fighter, which is detrimental to performance
Go to Options-Controls-map controllers
Select your stick, and check the "Advanced" box.
Now select the Z axis. On the left you will see a slider called "Deadband". Increase it a bit. Basically you will want enough deadband that not every X and Y axis movement will move your rudder too. Tweak it a bit to find the smallest deadband value you are still comfortable with. And learn to move your stick without twisting