Jordan is not the best ever fantasy writer and does not write the best and most nuanced characters, that's true; he doesn't compare to the likes of Kay. Nynaeve is no Dianora, and due to Jordan's extraordinary amount of PoV characters, we sometimes get PoV characters that don't have much depth. But to say he doesn't write any better characters than Brown on the whole is beyond absurd. Brown writes page-turner thrillers with the plot and the conspiracy theories overshadowing everything else, with character development way down the list of priorities. Even Langdon's character isn't really all that fleshed out, and even the short paragraphs that help describe his character and give him background are often plot-driven, like the story about falling into a well as a child to explain his claustrophobia. Whereas Nynaeve's character, to take your example, had some depth from the start, with various conflicting motivations and feelings - more so than comparable characters get in most other fantasy, to be honest, even if it obviously doesn't compare to more literary works - and went through some more or less believable evolutions as the story went on. You don't have to like the character to acknowledge that.

Now of course that doesn't mean Brown couldn't write better characters if he tried, to some extent it's his chosen genre that prevents him from fleshening characters out very much. But your statement that "Jordan's characters are just as two-dimensional as Brown's" is some fairly bad hyperbole and not even remotely accurate.