I think making the Nercomancer's attack speed higher might make him too powerful again weaker units. His attack is already very powerful if used correctly, and his other abilities make him a versatile hero already.
Meanwhile, Galadriel is 3 times Sauron's price, doesn't have an ability that can teleport her out of battle, has to be rebought if killed, and can't hit as many units as Sauron can with a single attack, so I think she should have a higher attack speed then Sauron.