Point taken but being more cunning and deceitful doesn't mean you are more powerful.
Case in point Sidious didn't surpass his masters knowledge as he even tells Anakin that he never figured out how his master prolonged his life but that maybe they could figure it out together.
Powerful is debateable. One man's weakness will always be another man's strength. But as far as knowledge goes, Sidious found his own way to extend his life through his clones in the novelizations of episodes 7, 8, and 9.
But, back to power. In the Dark Side, being more cunning and deceitful does indeed make you more powerful. You are alive, they are dead. Therefore, by the Dark Side, you are the rightful Lord of the Sith. Doesn't matter how they died. The Dark Side is strongest when it is owned by only one person. The moment Sidious killed Plagueis he became more powerful. The moment Zannah killed Bane she became more powerful. There is no honor or glory in the Dark Side. As Darth Bane was fond of saying, "Honor is a fool's prize, there is no glory for the dead."