Women still can't fight all that well in an era of muscle-powered weaponry. Few men would follow a commander who had never put her own butt on the line. Gareth Bryne and other generals had to earn their stripes, even if they were born to the nobility. Women like Elayne are the exceptions, because they represent a higher allegiance for their soldiers, but that is why Queens of Andor have both a professional military officer (Captain-General) and a personal champion/deputy (First Prince of the Sword) to handle the military aspects of rulership.

The Seanchan exceptions are due to their having institutionalized women in the military. Egeanin's mother was more or less the equivalent of the Chief of Staff of the Navy or Chief of Naval Operations. Women like Tylee have worked their way up to the top ranks and proven themselves, but there are few to no opportunities for wetlander women to do the same. The Aiel women similarly cannot advance, ironically because of their approach to gender equality. Since they give chiefs and roofmistresses equal but seperate duties, they need a mechanism for unifying that power and have chosen a family relationship as the means. Unless they are willing to let a Maiden marry a woman who can be roofmistress, a Maiden cannot rise to a command position. I would imagine a Maiden who was tactically adept might be given subordinate commands under a chief, but she could never be chief or battle-leader of a sept or hold, because that is tied up in the institution of marriage.