I don't understand you conclusion that Aegwyn is the greatest. If Azshara have been around for longer, have the guidance of the Old Gods and the source of increasing her powers, namely, Well of Eternity. Furthermore she have the motive of increasing her power, since she have increasingly grown stronger - I can't see it being a mere coincidence, rather it portends to explain her character, by being power thirsty and a central motive of her, would be dedication to magic in order to improve her power.