I think 10,000 seems rather too high - surely the Kin and the Aes Sedai between them contain a large majority of the Randland channelers, and of course with the Aiel we cannot just blindly assume that all the thirteen clans are of the same size.

But yes, since Nynaeve is apparently seventh on the list of named channelers, and since very strong women among the Wise Ones and Aes Sedai at least would likely have been mentioned by now, and hence been added to the list, she's certainly exceptionally strong by any standard.

At what position she would rank in a genuine world ranking, who can say, as we don't exactly have population numbers to make any kind of estimate for that. Not that it matters any.