AncientPower
The Chosen One
"I don't know for sure but I would imagine that there are no hard and fast lists about which Sith are the most powerful. "Most Powerful" would have lots of different variables to take into account. So it may be best to say that he was simply amongst the most powerful Sith along with Sidious and whoever else there may be. It you definitively say that one Sith was the most powerful then by definition any others that you create in the EU must be inferior so I doubt the continuity people make such absolutes about the powerfulness of the characters.""Agreed, us continuity people don't deal in absolutes. Only Sith deal in absolutes. With that said, we'll often need to come up with stats or rankings for gameplay purposes. These are for gameplay purposes only. Stunt coordinato Nick Gillard had his own lightsaber ranking, but even the use of this ranking system is limited because it was only the major characters from the prequel films that he ranked. We never expanded on that ranking system." - Leland Chee
The entire claim that Chee had some purview over the web supplement that he personally maintained is debunked by an actual quote from the man himself. Clearly stating that they don't do 'Darth Vader is more powerful than X.' rankings. Therefore attempting to use him to validate the claims made in Cory's web supplement is false.
Moreover, if you want to take Cory personally clarifying his stance as somehow removing the ambiguity of the quote at hand. Then we have claims from actual SW writers Drew and Tom Veitch. Clarifying statements that place Exar Kun above both Revan and Malak, and putting Kun up there with Sheev.
Then if you go into actual lore, we have canonical accolades putting Exar Kun up as the Sith GOAT until we get to SWTOR Tenebrae.
Then we have actual feats, in which Kun utterly humiliates Malak.