The Shaido have been slaughtered and run off and the Prophet and his minions are dead. those two situations could have caused a lot of problems during the Final Battle as armies would need to be used to address their chaos. We know that Perrin has also reunited the Queen with her son Galad and we suspect in the next book that the Children of Light situation will be reconciled to some extent so that they will be at least useful in the LB. Add to that the meeting and deal with the Seanchan and their subsequent battle with Trollocs and that deals a serious blow to the DO as he had the entire Seanchan forces hoodwinked as to the existence of such creatures.

As much of a pussy as Perrin is his actions have had a lot of indirect effect by taking care of problems that Rand would have had to spend time doing (and thus not preparing for the LB).

But, others have played major roles too as others point out. I just think Pussy Perrin's accomplishments are overlooked.