"The most powerful Sith Lords possess a talent for the dark alchemy of the Sith. The Emperor, like Naga Sadow and Exar Kun long before him, became a master of manipulating the genetic building blocks of living creatures through the dark side. Over the millennia, many creatures have been broken, twisted, and rebuilt by this evil power."
This quote is inherently different from the Wizards of the Coast quote:
"The Star Wars universe has created some truly vile dark side villains. Have you ever wondered what would happen if the most powerful Sith Lords duked it out for supremacy of the galaxy?"
For one, the first quote doesn't specify what Sith "the most powerful Sith Lords" is referring to. Thus, a broader and looser interpretation is possible. The latter quote, by virtue of the content of the source, specifically refers to Darth Sidious, Darth Caedus, and Darth Revan exclusively. The quote would have to be fundamentally changed to mean "some" if referring to the latter by virtue of a select number of Sith already listed, whereas with the former, nothing is solidified and thus alternative views can be established.
The quote would specifically have to read...
"The Star Wars universe has created some truly vile dark side villains. Have you ever wondered what would happen if some of the most powerful Sith Lords duked it out for supremacy of the galaxy?"
... in order to convey what is being suggested. The first quote doesn't, again, since the generic statement doesn't attribute a specific number of Sith to its name.
The Wizards of the Coast quote is essentially saying:
"The Star Wars universe has created some truly vile dark side villains. Have you ever wondered what would happen if the most powerful Sith Lords: Darth Sidious, Darth Caedus, and Darth Revan, duked it out for supremacy of the galaxy?"
The whole premise of the source is specifically pitting the most powerful Sith Lords against each-other. Thus, it is only logical that the Sith listed would therefore be the most powerful Sith Lords. It wouldn't make sense if the source was listing the #1, #7, and #12 most powerful Sith Lord, yet emphasize that the battle that is about to play out will feature "the most powerful Sith Lords." Wizards of the Coast has miniatures for Darth Krayt, Darth Vader, Darth Nihilus, Exar Kun, Ulic Qel-Droma, etc. They could have used these characters for this confrontation if they so wished, but they instead opted specifically for these three, obviously because these three are, in fact, the best.
By arguing otherwise, it's the same as saying you're about to gather together "the most powerful Jedi" and you get Luke Skywalker, the Hero of Tython, and Obi-Wan Kenobi. In contrast, my interpretation, following the logic and intent of the source, is gathering together Luke Skywalker, Yoda, and the next best Jedi in order to provide "the most powerful Jedi," not just "some of the most powerful Jedi."