Well... that's been generally accepted as the main explanation for many years now.

The decline is caused by the fact the Tower has stopped recruiting, and it's reputation isn't what it used to be and thus less attractive, so fewers candidates must come to be tested yearly, increasing the percentage of women who could learn but never trained.

However, the genetic decline has been confirmed as real by Jordan as well. The AOL era had about 3% of people with the genetic potential, the New Era had seen a decline to around 1%. The ability is being breeded out of humanity, just nowhere as dramatically or rapidly as some AS believe. It's still nowhere near extinction.

This is the result of:

- No Aes Sedai bearing offspring. They recruit most of the female sparkers on the continent, so if sparking has a genetic component, it is an ability which is slowly disappearing (though it doesn't take sparkers to breed sparkers... eg: Nynaeve's parents), especially since:

- The Aes Sedai and other groups have been killing all the male sparkers for 3000 years. They have now become really rare now, and the women are becoming rarer too. The great decline in male sparkers over the centuries confirms that this genetic characteristic is being culled out, and this in turn confirms the same happened to women in the main continent, because the AS don't have offspring.

- The Kin has recruited a lot of the WT rejects, so a large amount of women who seek to join the Tower and are rejected (far many more than women who manage to gain the shawl) also don't bear any offspring, as the Kin forbids it.

That leaves only the Windfinders, who have children, and the Wise Ones. The Sea Folk only remove the weakest sparkers from the gene pool, sending them to Tar Valon. We don't have exact or even approximative numbers, but it seems the ability is more present in these groups (they may be close to the AOL percentages still), it's not only the fact they manage to find everyone who could learn. These cultures have removed only the male sparkers from the gene pool, while the continent also removed the women.

The decline in strength is largely an unknown, but all the signs point not to genetics but to the Pattern, because very powerful channellers are reappearing as by magic all of a sudden, after a very long hiatus (over 1000 years...). IMO, The Wheel has kept in store for the era of the LB all the most powerful souls (from the transmigrations, we have confirmation that strength is determined by the soul, not the body - the last unknown was what happened to Lanfear, but the "not strong enouugh body for her full strength" theory has been crushed by TOM).

The Wheel may have began to reinsert some of those souls around 400-300 years ago, depending on cultures. Alivia is such a case, so is Cadsuane (the most powerful woman in a long time at the Tower), Romanda and others. And more recently, all hell broke loose with Sharina, Elayne, Egwene, Nynaeve, Shalon etc. - and of course all the men.