He is a vital character for the scene. Representing the moral facet in that scene. Rand is angered and under sever trauma, as well as emotionless due to the void. Perrin is there to serve a "humanitarian" POV. He was there to muster the forces and try to save Rand. The fact that Taim bounced in there and took the field doesn't mean he was the hero of the day. Perrin and company went into that battle knowing their only hope was to cut through and hope that Rand could make a gateway out. Perrin was willing to die for the cause of the DR. Taim and dozens of Asha'man came in and slaughtered the aiel with relatively few casualties. He also was there to urge Rand to stop the unnessisary loss of life. Had he not been there how many thousands of lives would have been taken that day. As far as plot relevance it showed the two facets of Rands moral struggle, something that climaxed six books later.