Yeah, that's all wrong. For one thing, RJ said strength is distributed over a bell curve, not strength levels. You're plotting the wrong data points.

That said, obviously each level corresponds to a range on the strength scale (whatever it was in RJ's, we can take it to be 1-100 and it will still work the same). The 21 levels are distributed over this scale. We don't know if each level represents an equal interval in the strength scale, but assuming we do, we'd expect a peak around 10/11, which is where you find it. However, you also need to note that the sampling in that list is atrocious. We tend to see and hear more about stronger Aes Sedai and very little about women too weak to become AS. That definitely causes skewing. Plus, the list is very subjective, and tries to make quantitative differences between "strong" and "very strong" and such terms.

RJ spoke of the same bell curve holding now. He said strength was distributed over a bell curve. That 67.5% of channelers in that curve would be strong enough to be Aes Sedai. That this is true only in the modern age, since in the AoL, anyone could become Aes Sedai. There's no doubt at all that its the same bell curve.