Kaan's brotherhood would, IMO, eventually lead to a complete strife for power and civil war by some ambitious sith, but Sadow's faction is held together because they believe him to be the rightful ruler to the throne, so it's more stable.
Well, minus Sadow's apprentice and Ludo Kressh and his followers. Remeber, the apprentice tried to turn Sadow over to the republic while Ludo Kressh attacked a retreating Sadow with a second sith fleet that could have been used instead to fight the Republic or at least allowed for a fighting retreat that kept a larger fleet intact. Sith by nature are traitors and power hungry. The only sith who recognized Sadow as ruler where the traditionalists, the weak, and the sith who sought power working with him instead of Kressh.
I agree with everything you said I just wanted to clarify this.