No, but Janus is a reliable source. Unlike some people...
And we have to look at the breaking of his will part, because if it can't be broken he can't die. His willpower is all that keeps him alive. Revan is clearly the more powerful of the two, but if he can't break Sion his will he probably can't win. So its a very important factor in the fight.
Debatable yes, do you have prove for it? No. Is it possible? Yes. But by what? Huge energy blasts.. Revan can't do that, you would need somebody like Kun. Force storms that destroy planets? Again you would need somebody else like DE Sidious, draining the life from him? Draining his force powers? Nah you would need to be Nihilus to do that.
Okay really the only chance Revan has is draining the life from Sion or breaking his will, since the first one might or might not be possible the second option is far more likely and important. And therefor the one we are debating, its Revan his biggest chance.
I think Sion would continue, he said himself to the Exile that he could die a hundred times and still rise, either he had experienced it or mabey that's just describing his power, but I don't know what Revan could do that makes Sion loose faith.
How can you defeat him without saying anything? Each time you strike him down there is a dialog, you have to say something.
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Revan is charismatic. Revan is the only other person aside from teh Exile who has ties to Kreia (Revan was Traya's padawn at one point). He is a good judge of character and motive. Sion would eventually let something slip, and Revan would capitalize on that fact and break Sion's will to live.
Well I never did it, but I heard it could be done, if its true or not I don't know. Wouldn't surprise me... But still Kamikz you have to remember a few things. Sion gave himself away against the Exile, he would probably do the same against Revan. Feeling superior undefeatable and thinking that he could actually win. Like he thought against the Exile, then superior lightsaber skills and force powers will beat him back into the ground until eventually he says to much Revan uses that and kills him. Sion could only lose his will against 3 people, the Exile, Kreia and Revan. And I don't think he would be able to stand against any one of those in a fight purely because he's an idiot and would say to much.