Seeing Madaras complete susano'o in the spoiler in this thread:
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It really makes me wonder.. how the hell did Hashi manage to beat him? Its quite the damn feat seeing as all we've been told about hashirama is that he can throw trees and heal himself without seals. Its defiantly an incredible feat if you ask me.
You have to keep a few things in mind:
1) Edo Madara is invincible. Several of the attacks he has used (meteors) would have killed him or hurt him if he were still alive. Oonoki's Jinton would have killed him if he were alive and didn't let himself get hit by it. Other attacks that would have injured or killed him would have had to be dodged.
2) During their battle, Madara either did not have rinnegan or chose not to activate it. This means his immunity to ninjutsu wouldn't have been available, neither would be the meteors, shinra tensei, or any others of those techniques.
3) As we saw with Sasuke, Susanoo requires a large amount of chakra to use and to keep active. Kabuto has completed Madara "beyond what he was in his prime". That means more chakra, hashirama's cells, etc. When he was still alive, Madara's chakra reserves would have been lower than they are now and spamming Susanoo would have been a sure way to lose a long drawn-out fight with Hashirama (Remember, as a Senju, Hashirama naturally had more chakra and more life energy. Madara would have needed to be careful to conserve energy to avoid being completely worn out by Hashirama). Itachi died from over-use of Susanoo. Sasuke almost died over-using it against the kages and later he was severely weakened and lost his ability to use it completely in his fight against Danzo. Mortals cannot use the technique for long periods of time (and, as we saw against the Kages and Danzo, the technique is not invincible anyway).
4) During their battle Madara didn't yet have Hashirama's power. This means no wood release, no powerful wood clones.
5) During their battle Madara did have the demon fox. However, we've seen on multiple occasions that controlling the fox takes a large amount of chakra and concentration. Plus, Madara didn't use a seal to put the fox inside himself and use the fox's chakra as his own. This means he would have had an additional chakra expenditure without gaining additional chakra capacity.
It's really not so hard to believe. Hashirama's wood release would help to keep Susanoo at a distance until Madara ran out of chakra from over-use of susanoo. At that point Hashirama would have conserved more chakra and would still have deeper reserves than Madara and would have won easily. The alternative is for Madara to NOT spam these expensive techniques, and stay in close hand-to-hand combat where he can more efficiently use chakra and keep up with Hashirama for a long battle.