The major flaw with RJ's character Demandred is in the amount of screen time he has been given. In trying to keep his "identity" a secret for so long we've seen almost nothing of him except a few glimpses in Forsaken gatherings or at Shayol Ghul. We've had more than 10,000 pages of the story so far and practically nothing on Demandred.

It is so late in the series that the only way to make Demandred not be a total waste is if his identity is revealed early in ToM and we see him leading the Shadow's armies or something similar for the next two books. However, the story seems to be told from the good guy perspective and so I think there is little or no chance of seeing major portions of the story told from Demandred's point of view. Thus, I presume that the next two books will see very little of Demandred.

When it is all said and done, Demandred's character will have been wasted by not giving him more screen time.