If we were to use the example of the military and the ranking system, the officers are in the direct chain of command; they issue the orders and have direct authority to act as representatives of the United States, which is why they are given commissions that are signed by the President. The NCOs actually carry about the day-to-day tasks that keep the services running. But only a foolish Lieutenant would not listen to the typically more seasoned Sergeant; one, because obviously the NCO has experience that can be valuable in real life and two, because the NCO is the person actually carrying out the Lieutenant's orders.

And you must also keep in mind that even the newest Lieutenant outranks the Sergeant Major of the NCO Corps in terms of the hierarchy of military forces precisely because the commission they received is a point of demarcation in the ranking system.

Though Warders may disagree with their Aes Sedai, this is very rarely done in public for the practical reason that to the public eye, the Warder is the right hand of the Sister. Moiraine and Lan presented a united front to the world precisely because ultimately, she wasn't a fool, and he backed up her decisions.

A Warders' advice may be welcomed in private, but in public, this is tantamount to questioning the judgment of a superior in their ranking system and it undermines credibility. to go back to the military example, a new Lt. often makes mistakes, but if they have what is considered a good NCO, the NCO will accommodate the mistake in such a way that the order is carried out in the way it was intended to.

In terms of the White Tower as an organization, Warders are never truly part of it in the way that a Novice, Accepted or Sister is because these women form the body of the White Tower while Warders feel a calling to serve them. This is, to put it bluntly, an unequal relationship and it seems it only approaches a partnership in terms of private interaction and intimate knowledge of the other person.