If the netgaining strats didn't have a higher growth potential than the war strats there would be no reason for anyone to play them. The game was designed as an example of efficiency through specialization.

In this specific case: Dictator has an large warfare advantage and in order to balance this a restricted ability to grow. It's intended to be a post-growth stage government and does that very, very well. Commies are basically the opposite: high early growth potential with no viable endgame.