The "villans" have always felt largely irrelevant with regard to the story. It is primarily a coming of age/good vs evil story, with the main protaganist being Rand, and Mat, Perrin, Nynaeve, Elayne and Egwene to a lesser extent (though not by much).

Yes it is frustrating that the villans have been revealed, explored a little, and then dumped a few books later. But the same can be said with regards to lots of characters. Loial and Thom were big characters for a while and it appeared Loial was going to have a big part to play in the story, but he has been sidtracked and all but ignored in the last 4 - 5 books. Though I feel the Ogier - not necessarily Loial specifically - will have a big part to play at the last battle. And this is one of the problems of a sprawling, unwieldly narrative, characters are built up, then ignored and when they turn up again I certainly think WTF!

Loial, Lan, Thom, the Seanchan, Logain, The Black Tower, The Forsaken, Aviendha have all had big parts to play in the story, but due to the constraints of the books' length they have been somewhat sidetracked at times. And more than once this has left me feeling frustrated, especially when large amounts of time were given to the Perrin/ Faile plotline, the Elayne succession and the rebel tower yawn-fest. Where we had pages of sniffing, dress descriptions and non plot progression.

Better editing and a more focused apporach would certainly have eliminated some of this. But then this approach is what some people like. I don't know why, bet hey ho.