The problem with the Aiel wasn't too much power. It was absence of a structure to that power. They got united for the first time under Rand, and found that they were this incredibly powerful nation, militarily, and ended up misusing that power.

If, instead, they had fragmented into two, or even more factions after Rand was gone, do you really think the situation would have gotten better? %0 roving bands of Aiel, many of which decide to attack the Seanchan and other nations for want of anything else to do... would that really have been better?

Let us stipulate that Egwene and Elayne will both be succeeded by power hungry tyrants. If these two start fighting each other for influence, would the situation be any better than if they were tied together by the actions of their predecessors?

What if one is a tyrant and the other is a sensible and wise leader? They may check each other before too much damage is done as allies.

In the end, none of these scenarios matter since no one has any way of knowing. And since no one can know, asking people to wilfully dilute power to prevent the possibility that they may be succeeded by tyrants is ridiculous. Far better to introduce checks and balances in the system to make the tyrant's job harder.