That only works up to a point. That point being where the engine is so big that it is the plane's entire payload, in other words, your plane is an engine with wings on it. At that point, using a bigger engine just means you have a bigger flying engine. The increase in the plane's weight cancels out the extra power.
I doubt that any engine will make a trainer go 200 mph. About the only way you could make a trainer go that fast is to check it in as baggage on a airline flight.
If you want to go faster than 100-120 mph with a model, the airframe has to cooperate with the engine by being designed for low drag.