the Author laid it out as a fact of HIS universe. We have to live with it.

Accept the fact that the Forsaken are not that much stronger than everyone else ... as I've stated a million times, they don't HAVE to be ... raw power is nearly a meaningless conversation when the only facts we have are:

1. Lanfear is as strong as a woman can be
2. Morgase is as weak as a woman can be

This means there MUST be an equal number of SD between Morgase and the Mean as there are between Lanfear and the Mean, but it says NOTHING of actual amounts of the Power each level represents. The misstep here is that we are talking about % of total as the same thing as amount of power. Lanfear is 100% of the maximum strength, but can likely handle many hundreds of times the amount of Power Morgase can handle. Moiraine IMO can handle roughly half the volume of Lanfear, but that may not mean she is the Mean on a Bell Curve. She may well be as much higher from the evidence, it's possible that she is several SDs above Mean.

3. Daigian MUST be stronger than about 40% of women and 30% of Men
4. Daigian can handle roughly 1/3 as much saidar as Moiraine

This says nothing about their relative places on the BC since we cannot reliably place either of them. IMO they are probably around the same distance from the Mean but that is purely speculation.

5. Egwene is roughly equal to Amys and Melaine combined.

This makes her somewhere along the lines of 1.75x Moiraine in terms of volume of saidar she can wield, but again, there is no way to know where she falls on the BC aside from the evidence in the books which makes her an outlier of more than 2 SD from the Mean. This also means that she is probably as rare as a woman like Alise or Sorilea who are also outliers on the weaker side of the Curve.

No math formula is going to magically make all of the tidbits we have work. But I will stick to the author's quote on the existence of a BC as he is in effect "god" in terms of WoT.