OK, so Rhye wants stability to be more punishing for the big empire builders. How about a lifeline: the ability to inject a boost of x stability (depending on how much gold you have to buy it, the larger the empire, the more costly). This could be imagined as a temporary rally due to "patriotism," stringent measures (such as all-out-mobilization during times of war and granting dictatorship), or just plain good luck. Rome did it (Cannae was a pretty devastating defeat), Russia did it (during the WWII), and these are historically large empires. Or, if you don't have enough great people to start a GA, sacrifice half of them to get a stability boost. God knows how many times Chinese dynasties on the wane have been granted an extension due to the efforts of good ministers.