A thing like Watson would always win if we brought it into Letters and Numbers. No one on Earth would stand a chance.
Why?
Letters Game: Install Anagram maker.
Numbers Game: Install some mathematical solver thing that is about six hundred million times more simple than the algorithms that Watson uses to decode speech (in the clues).
Watson decodes speech - that's what it's designed to do, while in Letters and Numbers - we're just giving it raw data to work with, in essence. No puns, no tricks, no obscure references to decode...