Board Thread:Theories and Speculation/@comment-27233105-20160307210530/@comment-681696-20160307222705

Edo Tensei doesn't revive people at their full power, all edo tensei zombies were weaker than when they were alive, however between Orochimaru's attack on Konoha and the SWW4, Orochimaru had improved the jutsu to the point that the Hokage lost only a small amount of their power.