Wrong. It is considered a triumph because the ultimate goal was the extinction of the Jedi. In the Book of the Sith, Darth Bane even states: "If you are not willing to accept the fact that your apprentice will kill you, you are already a wound in the Sith Order, and your contribution is not needed, and the Sith have suffered a fateful blow." In essence, the Sith knew that they were going to die, but they had to give the Apprentice no quarter what-so-ever. If the Master gets poisoned, that's their own fault, and the Apprentice outsmarted them, which was a big part of the Rule of Two.
On top of that, the Sith Master would teach the Apprentice, but not share the slightest bit of power, thus making the Apprentice work for it.
Also, why in the world is this a topic? The Rule of Two was better than any method before it, considering that in the lore it worked. When it comes to the Sith, no other Order comes close, I mean crap, even Darth Krayt's Rule of One had a betrayal by Wyyyrlok III.