There is a case to be made about large empires in general being too stable. Ottomans also fall in this boat, and a united India is basically Russia instead of the fragmented feudal empire it was. I feel it has a lot to do with there not being enough expenses in this game, because running a massive empire in this game with little to no planning makes you money. Of course, you can actually think and plan and make a sodding ton of money, but not every player thinks or plans, and certainly the AI doesn't.
European empires historically stayed big and powerful as long as they did because they were INCREDIBLY rich, and relatively decentralized. Any hole or leak in the Imperial administration, they threw money at the problem and it would fix it. Major Asian empires, by the time of their decline, were facing financial crisises. The Ming suffered a silver shortage, and could not compete with Portuguese trade. Coupled with some nasty natural disasters (and natural disasters should be scripted events anyway), and draconian measures to attempt to "make China great again" at the expense of the population, the Emperor basically lost all respect and trust and the Manchu found themselves invading and conquering a shadow of the former Ming (and causing the bloodiest war before the Taiping Rebellion and WWI, so it's not like the Manchu invasion IRL was that easy either).
The game needs to do more to address the importance of money, and big empires should only stay big if they can pay their bureaucracy. This would make playing as blobbers more challenging, and encouraging planned expansion (actually looking at trade flow, development, and resource production to decide on expansion), domestic development, and overseas imperialism. However, improving EU4 finance is easier said than done, because it still needs to be fun and easy enough for a new player to take time to learn it. Ming stability is not only a problem today for other nation players, but also Ming players (at least myself) who see Ming as more of a cheese-fest than the Great Dragon Throne who is the center of the world.
