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

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