I dont know if you all noticed but Hiruzen is old and not in his prime. I thought Edo Tensei revived you at your stongest point. If this is true then there shouldnt be anymore prime hiruzen references because Kishi just showed us that the 3rd was stromger before he passed. If you say its because they want his knowledge and that is why he is old that isnt true, look at Madara he remembers everything and he was revived in his young state.