Exar Kun and Ulic-Qel Droma vs Darth Revan and Naga Sadow.

I'd have trouble putting Kun that high. Especially considering Yoda's already above Kun in saber dueling, being the best saber duelist the Jedi order had produced.
when it comes to DE, it's pretty much made clear Sidious reached a new plateau and almost became a Dark Side god

Yoda - the strongest saber dueler that the order ever produced? Hardly.

Considering it's outright stated he was...

I think that too, Lightsnake. He seems to just have more raw power than any of the others, even Kun. However, this doesn't have to do with DE Sidious. Kun is the most powerful one in this fight, and could beat Naga. Ulic and Revan are pretty close, not to mention that Ulic and Exar probably have some kind of synergy and work better as a team then Naga and Revan would. I'm going to say that Exar and Ulic have a solid, while not effortless victory.

I believe Kun could do this alone.

ok everyone says ragnos is the strongest so why didnt one of these other guys you say is stronger just kill him and take his place and why didnt they just tell his ghost to go bug someone else.