"The holocron belonged to the ancient Sith Lord Darth Revan, who was the first to realize the flawed logic of training more than one apprentice. Through the gatekeeper of his holocron, Revan taught Bane how any master that trained multiple apprentices was a fool. Bane learned from Revan's holocron that, in times past, the students would seek to destroy their master and claim the title. By joining forces and combining their lesser powers, they would attack and defeat their master."Actually the Rule of 2 came from Darth Revan Darth Bane just reused it for his era, so the Rule of 2 originates before this game
Revan did not start or put into practice the rule of two, he was smart enough to see the flaw in the system yes, but he only did it to train one apprentice at a time, to prevent them from teaming up. It was Darth Bane who broke the Sith and remade it into the ones who follow the rule of two.