This, among some of the other things have begun to make me question the dark one's intentions.
I get that "evil is self defeating" but what if it's more than that.
Semirrhage was, for instance, reportedly ordered to send shadowspawn to fight shadowspawn in Tear. This isn't self defeating, this is rather intentional.
What if the Dark One was the Victor, not because he succeeded in destroying the pattern or because he swapped with the dragon, but because he acheived what he set out to achieve in raising Rand.
The way the DO communicates to Rand after he touches the shade of shaidar haran is almost like that of a teacher in the way that he criticizes rands attempts.
Perhaps the last battle is the dark one's way of repairing the bore himself, entrusting only a worthy adversary to wield those powers necessary without ruining creation.
Think of how much the Dark One's servants pushed rand into the man he becomes. In the portal worlds and in egwenes accepted test we see a world where the two Rivers is never attacked and Rand eventually succumbs to the dark one's taint. If he really wanted to deal with Rand then he would have simply ignored him and let his very existence destroy him.
For some reason the dark one needs Rand to be the dragon.