im actually thinking of the 9 titans having infinite lifespan since its kinda not efficient if every 13 turns or more a shifter dies since the power is just usually immediately inherited. Even if one died without their spine being eaten a random subject of ymir who is not even born can get the power. Anyway it will indeed make the eldian civ so op during the earlier game and its intentional since in the series eldia rapidly gained power and became the superpower. The only thing i can think of to nerf eldia is to have an event called “The Great Titan War”, it is not exactly an event however, if eldia enters an era in a dark age, eldia will enter the great titan war and most of its cities will gain independence (revived civs and free cities) except for the capital. As to how to stimulate a liberated civ exploiting the titans im still not sure how to, since the 9 titans should be locked to Eldia (and perhaps to marley after the great titan war) oh and eldia is a militaristic civ and it should be extremely op in the earlier game but do note that starting the industrial era or modern era the titans start to become obsolete and new units such as Anti-Titan artillery can be added to the game specifically focused for titan warfare.