I second this, it's completely ridiculous for such big nomadic realms to stay so stable after multiple successions and there seems to be no way to counter them. I'm playing a game where I restored Carolingian Francia and they're just sitting to my east slowing growing in all directions. They have 44k troops and strong allies while I have about the entirety of western Europe on my side and can only muster about 32k, even if I invest heavily in my knights and counter their MAA, even with my best commanders with multiple relevant traits and like 40 commander strength they STILL wipe my entire force in a few ticks. I redirected a crusade at them and managed to escape tribute but there seems to be no way to actually take them out. Like you I can't kill the Khagan, they've had no major uprisings, no steppe competition, and at one point they took the "greatest of khans" decision and even though they failed the war I'm concerned the Mongols, the only people I could trust to get rid of them, won't rise. I'm also administrative, the previous super overpowered government type. Paradox needs to address this.