I doubt very much that Sanderson had it in him to portray Rand this way without excessive notes from RJ. And I'm very certain RJ left tons of notes on this. There's something entirely believable about this Rand. As Nynaeve points out, it is so easy to slip into the mindset that he is only doing what is right, being entirely rational.

It was the build up to this character that allows us, at one point, to actually see reason in a man who is mad. That was the truly scary part of the story, and it has always been heading there.