I always assumed Nynaeve at the top was a list he later revised as he decided to bring in - Edit 1
Before modification by darius_sedai at 27/09/2012 06:40:30 AM
The reason I think that is that Brandon said there were two lists. In one, Nynaeve is pretty much at the top. In the other, there are six above her. That's what made me wonder. Maybe RJ had the second list for the pre-Cleansing part of the series, and the first for after that (assuming Nyn got her full strength then).
Other uber-Channelers, or that at some point he decided he thought Nynaeve's character may be more compelling if she wasn't the absolute Strongest women. I have to say her character is better to me since learning that she isn't the top dog. Nynaeve is a bit of a bully! She needs some humbling things.
Ad RJ did say at one point that Nynaeve was right in the middle of Forsaken women Strength