No he isn't. In the victory speech after the SC win, he pointedly said just the opposite.
I think you misunderstood what he said.. he didn’t say he wasn’t a great debater he said it was his message not his debating skills that won the day.. he brags on his debating skills all the time especially when taunting Obama for the Lincoln/Douglas debates where he’ll just use his knowledge and ability to get across his views(ie. superior debating skills)and Obama can use his teleprompters