The game will always heavily flawed as long you cannot conquer the green area within 30 years.
What I hate most in the Paradox game is that even you occupy all provinces your enemy arbitrary the war score cost prevents you from annexing them. That isn't me advocating for blobbing, but highlighting the poor design choices. The game should make that kinda conquest expensive and very difficult, but possible instead of introducing a hard limit and calling it a day.
And after you have reaches a certain size, further conquest should become more difficult and the gameplay should shift to keeping your empire together. While the game offers things to do in peace, management of empires still isn't that hard, does little to actually discourage further conquest.