In many ways Cadsuane does fill the avoid left my Moiraine, though she is hardly a replacement character. You must remember that the two approach the world far differently - Moiraine relied on secrecy and general intrigue, whereas Cadsuane utilizes force (force of will, physical force, etc). Rand needed an advisor who was up front (or as genuine as an aes sedai can be); Rand no longer trusted aes sedai and, frankly, I believe he would have tired of Moiraine's antics much sooner than he did Cadsuane's.