The Sith could grow their numbers significantly and root out corruption and paranoia, and all around be way more powerful and efficient if they would just get rid of the rule of two. First of all, the Sith aren't inherently corrupt, nor should they be, at least in organization. The Rule of Two creates an atmosphere of paranoia, scheming, suspiciousness; the master is always paranoid of his apprentice and the apprentice is always anxious of being replaced, which usually also means death. (Ex., Maul, Dooku, and Anakin) Maul is replaced by Dooku, then Dooku by Anakin. Then it was Sidious's plan to take Luke as his apprentice and kill Vader. As was it Vader's plan to take Luke as an apprentice and kill Sidious. However, other Sith existed, and there were loopholes. The inquisitors are Sith, but not apprentices. But they answer to either Vader or Sidious. Why not just have all Sith band together to form another Sith Empire? Why instead backstab and scheme and ultimately rely mostly on non-force sensitives to build your empire as Sidious did? Surely, it's better to have all Sith work together and be friendly with each other? The Sith code doesn't say that Sith have to be rivals with one another. Also, why didn't Sidious recruit Sith as extensively as the Jedi did? I mean the kids are kidnapped and indoctrinated by the Jedi as is, so swaying young Jedi or at least doing the same thing doesn't seem hard. You might bring up secrecy, but the Jedi were oblivious to Sidious and the true nature of the clone army, so it's not impossible.