Of course, few Sith Lords achieve very much at all. But that's because all they try to do is wage war. Which they inevitably fail at. Bane actually saw that war with the Jedi was bound for failure. So by putting forth the Rule of Two, he actually achieved something greater than past Sith Lords.
That's called stubborn idiocy, if he had admitted his defeat he could have done something for the Sith e.g. what Freedon Nadd did, impart his knowledge to a worthy successor. But he was too absorbed in his lust personal power to see the bigger picture. That's why he failed in life and that's why he failed in death - Bane would not have been impressed. Bane being a real Sith Lord, he realised is own existence was merely a component in a greater design, as such he actually achieved something. What did Kun achieve? Nada.
But that depends on what one could consider 'accomplishments'.