Why has any of this got to be true? Cadsuane makes it clear that it usually falls to the weakest women to hold shields. Which means it was women only somewhat stronger than Daigian who held Logain (and we know such women exist, from Egwene's comments on the women who went to test the residues after the Cleansing). Five such women could barely hold Logain, and Nynaeve could barely hold Logain. Seems clear that Nynaeve is about 6-8 Daigians at most.

And there's a simple reason why we can be fairly sure Egwene and co. aren't much weaker than Nynaeve. Not once do any of these women (especially Elayne) think about how much they need to defer to Nynaeve, even in public. Yet Elayne, for one, makes strength comparisons with other AS to determine the level of deference all the time. That's a subtle clue that Elayne is not much weaker than Nynaeve.