There's an actually a much easier way to go about this and that's to interpret any quote/statement in a fashion that renders the least amount of contradictions. Obviously, if we are to conclude that Bane is literally more powerful and knowledgeable than anyone who has come before, that raises a great deal of contradictions and makes the Bane a complete numbskull throughout the Bane trilogy. Who needs the rule of two when you've got nigh-immortality like Vitiate's and force-drain capabilities like Nihilus? There are much smarter ways to get revenge on the Jedi and rule the galaxy as opposed hoping that no Sith apprentice ever ends the rule of two in the fashion Vader did.
On the other hand, if if we to take that quote as a reflection of non-legends characters, a retcon (in case future discussions should be premised on pre and post-retcon versions of these characters), unquantifiable puffery or simply, as Palpatine would put it, a different "point of view" on what constitutes power and knowledge (something future writers are welcome to clarify on), the Bane Trilogy makes sense, as do subsequent works.