Firstly, channeling strength IS linked to genetics. It is blatantly incorrect to say that it is solely linked to the soul.

In fact, it is linked to both the soul and the body. If Lews Therin's soul was reborn into a body that does not have sufficient strength, he will be weaker in the One Power than in his previous incarnation.

So yes, a weaker channeling gene pool will serve to reduce average strength.

Secondly, great work in applying a Bell Curve to the estimated channeler strengths of known channelers. It indeed clearly shows that the curve now spikes way lower than it did in the Age of Legends.

Furthermore, RJ has confirmed that 62.5% of female channelers are strong enough to pass the Aes Sedai test (meaning they are as strong as Daigian or stronger). This means that only 12.5% of channelers lie between Daigian and the average strength channeler.

We know that Daigian is roughly one third as strong as Moiraine. And we know that Lanfear is FAR more than twice as strong as Moiraine (meaning that Moiraine has to lie below the average strength channeler).

All of this tells us that all modern Aes Sedai come from less than 12.5% of the total female channeling population. This HAS to be the case, because if 37.5% lie below Daigian, then 12.5% lie between Daigian and the average strength, and if Moiraine lies BELOW the average strength, then all modern sisters who fall between Daigian and Moiraine come from LESS than 12.5% of the total channeling population.

There it is. Irrefutable, if you believe in the Bell Curve hypothesis.