Then Darth Bane comes along with a rule that screams idiocy, by definition of being only two the Sith are extremely vulnerable as soon as they reveal themselves
I think you might be a little too hasty there friend.
When the Sith revealed themselves in Episode 1 after 1,000 years following the Rule of Two, and following Maul's death, the Jedi didn't even know If the master, or apprentice had been killed. Nor did they have any clue who else might be Sith.
While The Brotherhood of Darkness was strong, they didn't beat either the Jedi, nor the Republic. In fact they waged a centuries long war with them. The Sith Empire of TOR also haven't beaten either Jedi, nor Republic.
I can't actually think of, or know of any Sith Empire not following the Rule of Two that has ever decisively won over the Jedi Order, or The Republic. If anyone knows of another Sith Empire not following The Rule who managed to defeat both Jedi, and Republic please let me know.
During the Rule of Two however, Darth Sidious orchestrated both the destruction of the Jedi Order, and the Republic. Both more or less overnight.