I agree. The Man in Black, Dread Pirate Roberts, or Wesley (the one with eyes like the sea after a storm), should certainly have been on this list, since he defeated Inigo with the "I am not left-handed" trick (one of the oldest in the book). Clearly, his defeat of Fezzik and Vincini show that he would bring a lot more than mere swordsmanship to any contest.
Of course, like Inigo, he is motivated by his desire for revenge on Humperdink and to be reunited with Buttercup ... lacking that motivation, I'm not sure he has it in him to defeat any of these blades -- he'd probably rather just ride off into the sunset or agree to serve as their valet.
No good deed goes unpunished. -- (attributed to) Oscar Wilde