I posted this a while back in the Marka Ragnos thread and I think that it accurately explains how Ragnos and the ancient sith really wouldn't be too great in a 1 on 1 battle.
"How do you really think Ragnos would even defeat someone like Yoda. He wouldn't be able to crush him with the force like you have already said. Think back to the book Shadow Hunter when Darsha Assant (I think that's her name) mentions that her master used to force throw boulders with ease, yet struggled to lift up pebbles. The sith magics were clearly able to amplify the FORCE POWER of the user to perform extremely distructive powers such as blowing up stars, but FORCE CONTROL is vital for performing destructive force powers in a small scale, and seeing as there is no evidence of the sith having great control over the force and no evidence that the sith magics amplifying that aspect of the force, I am inclined to believe that the ancient sith would be able to do anything special in a 1 on 1 battle. The fact that the most powerful sith magic that can be used in small fights was Kun's amulet kind of helps my point. It also explains why Naga Sadow resorted to a swordfight with Ludo Kressh when he wanted to be the dark lord. Yet when he was in his ship, he used his destructive sith magic."