I would think that if one wanted to create a super assassin, the best thing to do would be to capture a male Aiel channeler, who after all go out wandering the Blight to die in a burst of glory, turn them to the Dark, give them a filter on The Power and give them the power to freely access T'A'R.

Instead, the Dark One merges two random people together who were, from It's perspective, just normal men.

This is why the Dark One will lose. Because evil is dumb in WoTland.