The thing is, it isn't really. Since the people of the world KNOW time is circular, there is no reason they'd call something THE last battle, instead of A last battle, or the last battle OF AN AGE or of a wheel turn or some such. So far the Aes Sedai kept saying how the prophecies are very hard to understand etc., but truth be told, most have been rather straight forward so far, when it really came down to it. There for I see no reason not to assume that THE last battle isn't just as plain. It's THE last battle. I also think Fain will play a big role, and I was reaffirmed by the first chapter published in the TOR website. The parts written in Ran'd point of view shows he's planning something BIG, and the way it was described shows it's not just the breaking of the seals and all that stuff that we already know.