Exactly. They need to be in the very first episode/season as major characters. They need to play extras as Emond's Fielders. They need to play Moiraine, and Lan, and Bran al'Vere, and Bayle Domon, and Min, and Morgase, and Elayne's brothers, and the major arcana Aes Sedai. LotR had some unknowns play major roles (Viggo Mortensen was largely unfamiliar before his role as Aragorn), and the seasoned actors like Ian McKellen and John Rhys-Davies were excellent choices to help act as teacher figures. If Viggo played Lan he would bring a LOT to the show, but there's the issue that people unfamiliar with the books would think it's a LotR spinoff if a well known LotR actor was involved, especially if there is already a LotR show in the works through the same company.