Engine size would probably only effect the speed at which the airplane counter-rotates to the prop-during a stall, not normal flight. Your airplane(specifically your choice of engine size) is not broke, so there is no reason to fix it. If your airframe can take the engine, I'd say keep it! The fix is not in the engine size but rather in usage of left rudder or less deflection. Like its been said, lots of elevator will put the wing at an angle of attack where it stops flying, and stalls-it has nothing to do with lateral balance, but physics. The air over the top of the wing is disturbed, and no longer laminar-destroying all lift. Ailerons would be useless at that point, rudder would stop the rotation which is caused by the torque of the engine.
I would keep the high rates on a dual rate radio and fly the airplane on low rates to get to know it. Chose the low rates based on your airplane, not necessarily the recommended deflection in the book. That's just a good place to start. It'll be a trial and error process untill the airplane stops snapping. My expierience is that every plane is different.
You may need more deflection for flaring when you land then your low rates will allow{(when your rates are adjusted right to fly at higher speeds without stalling the wing(high speed stall)}, so you may need to land with high rates, but be carefull so it doesn't bite ya', because it will still snap at lower speeds also.