First, Kahn made his decree as the Hero of Darkness, announcing that he would be the one to lead the entire Abyss Empire under a single banner for the upcoming Great War.
Then he started the whole self-comparison and started asked the questions that many already had in their hearts and minds.
Other than the Cult of Darkborne, the remaining two forces had no reason to relinquish their authority and follow Kahn's leadership without any qualms and misgivings of their own.
For all he knew, there could be a possible coup or a breach of trust later on, most likely when Kahn was in dire straits and in need of their full support.
Even with his powerful generals and the Chapter Masters, it was not a sufficient force to fight in the Great War. The majority of the forces would be fighting on different fronts, saints included; thus, there needed to be even more saints to maintain the order and protect the people as their strongest forces fought on the frontlines.
