What I'm saying is that Moiraine, a strong Aes Sedai, may not be above average for female channelers as a whole. She may very well be on the upward curve of the bell rather than near the top. A key point to consider is that before her time, there were three Aes Sedai near Cadsuane's strength level, and a few generations before that, we have to assume that there were more powerful Sisters above Cadsuane's level who died before she was born. Thus the White Tower truly is in a decline - perhaps at one point, when Aes Sedai were more respected and less political, it represented a diverse range of strengths, but it seems that as the years wore on and fewer girls sought out the Tower, they dropped below the female average.

I would say that Egwene, Elayne and Aviendha are right at the point where above average channelers start merging into stronger channelers but not much further beyond it - they are strong enough to always be considered powerful, but not exceptionally strong enough to be in the same class as the Forsaken.