Dual Sword styles even in real life were more often Defensive in nature. Often focused on switching between a solid defense and a fast offense before the enemy could react. Dual Swords in Nioh 2 excel in Blocking and allowing you to attack well after doing so, as well as keeping a low weight so you can dodge instead if you're confident. Meanwhile Axes are poorly designed for Blocking, and in general an Axeman had to rely on their armor for defense since any attack with an Axe leaves them completely open.