Brandon even told me at signing (well, rather the guy beside me who had asked him that) he'd seen the graphs RJ made in the notes...

RJ obviously used this as a tool to loosely distribute larger groups of characters.

There probably is an higher percentage of rarer strengths on both sides among WO and WF, simply because the ability is more common among them (they've not culled out the female gene pool among sparkers the way AS have done, and both group marry and have children).

For the rest, all evidence points to strength coming exclusively from the soul (what happened to Lanfear, discrediting the hypothesis it was a body issue ought to put that debate to rest. There's no oddity with Rand, nor with any of the transmigrated Forsaken who all have their exact old strength), so the bell curve would be very close to the AOL's, but in practice I'm guessing it would be very different as the percentage of women whose ability is found is incredibly low (tens of thousand aren't found in the Westlands alone), and the ability is less present in various groups because of culling. I suck at statistics, but my feeling is that the sample among AS at least is probably so small in comparison to Westlands women with the ability, that how the women get found is so random (relying massively on women deciding to go being tested... and they have such a small window of opportunity to make that decision...) there would be tons of aberrations, for e.g. for a few hundreds years, on a sample of only 1000 women, very few subjects with the rare strengths might show up at all.

How come women of Graendal's strength are so rare? Well, how many Graendal are there supposed to be anyway, in the current overall human population? A few hundreds, thousands, less?

We have no idea how big the SF population is, the Aiel are numerous. Those are the only two groups who find and train all their women, but both would have a lower percentage of channellers being born than in the AOL, as they cull male sparkers. In the Westlands it's worse thanks to AS culling out both male and female sparkers.

In Seanchan, they're also culling out male and female sparkers, and even more thoroughly than in the Westlands as all damane are found. The majority of their channelers, however, are never found (as channelers... they become sul'dam instead).

It would mean women in the rarer levels (high and low) would show and most of them are never found. Occasionally, a few of those would show up, like Talaan or the strongest WO.

Finally, there's a factor that is too overlooked: the Pattern.

It's rather obvious the White Tower has been "managed" by the Wheel. If its numbers have dwindled, and its average strength plummet, it's obviously in preparation for the LB. Souls have been kept in reserve for the LB era. It's no coincidence Siuan, Elaida, Aviendha, Elayne, Egwene, Nyaneve, Cadsuane, Moiraine all have the proper strengths to play their roles. The WT has lacked strong recruits for many hundreds years, and suddenly they return... tons of novices above average, some like Sharina from the very rare levels etc. The SF has some too, the Seanchan (like Alivia), the WO. All at the right time.

Let's not forget the Shadow once had 50% of all channellers and nearly won. It's no coincidence the current crop of channelers were extremely unattractive to the Shadow, if they had showed up and too early, Forsaken like Be'lal, Moghedien and Graendal would have snatched them up and train them as weapon, the Generals would have been more tempted to recruit and train, Ishamael would have put a lot more efforts into converting channelers to the Shadow. Etc. The whole "it's not worth it, too much work to train properly such women, not enough angreal to provide them decent strength" factors must have played out to an extent (instead of training them as fighters, Moridin used the BA as a political organ, not worrying overly about strength and training etc.).