Oh, the most convincing evidence we have for Taim being any one of the forsaken is the fact that he calls travelling by its name and that he has held of the taint for a long time. Did he call travelling by its name right away, or before he had time to talk to Rand? I can't remember. Holding of the taint for 15 years is not evidence. This is beause no one knows how the taint works. We don't know how much he channeled before he proclaimed himself. Maybe now that he channels a lot he'll be affected by the taint. Right now there's not enough information.