Sure.
For example, the Hand of Thrawn duology's publisher's statement says that "the New Republic faces its greatest [foe/challenge/enemy/threat] yet -- a dead Imperial warlord", in reference to Grand Admiral Thrawn. Though it is an out of universe source, the idea that in death Thrawn could be a greater enemy than the likes of Ysanne Isard, Sate Pestage, Warlord Zsinj, the Ssi-Ruuk, the Yevetha, the Disciples of Ragnos, Gilad Pellaeon, or Palpatine himself is simply implausible.
Not to mention, of course, that the line doesn't mention a historical context and that there were other so-called 'Sith' alive at the time. One could make an argument that the line was in context only. After all, the official website and the Complete Star Wars Encyclopedia reference Yoda and Palpatine as "the most powerful practitioners of the Force's light and dark sides" respectively.