The first hokage had the wood-style, which we've seen Yamato use several times, we've seen the first use in the fight against the third, and we've seen Danzo use briefly. There's more to that style than we seem to know, because Madara's plans with Zetsu seem to rely on wood style too.
We've seen the wood style be used as a very strong defense mechanism, creating living trees to get in the way of other attacks. Danzo was able to use his wood release to block an arrow fired by Sasuke's Susanoo, and Yamato used it several times throughout the manga to create defensive shields. We've also seen the wood release be used to trap enemies, like when the first used it to trap the third, or when Yamato used it to wrap up Madara. We also know that the wood release gave Hashirama the unparalleled ability to control tailed beasts. His ability to suppress and control tailed beasts would have been just as strong or stronger than Madara's ability.
We also know that Danzo used Hashirama's cells to boost his own chakra. This suggests that Hashirama either naturally had high chakra, or that his wood-release raised his chakra some how.
Madara came to the fight with the 9-tailed fox, but we know that Hashirama was in control of several tailed beasts himself, although I don't think we know exactly how many he had at the time of the battle. It's likely that he had at least one or two under his control, and was probably able to make use of their chakra. After Hashirama suppressed the Fox, He would have had some tailed-beast chakra himself, and Madara would not have had any. If he had at least one tailed beast under his control at the time, he would have been immune to genjutsu and would have had lots of excess chakra, more than Madara had.
We know that Madara had EMS. He would have had Amaterasu, Tsukuyomi, and Susanoo. He probably also had his space/time jutsu as well (we don't know for certain when he got it). He would not have had access to Izanagi yet. We know that EMS techniques use a lot of chakra. Even in the EMS, he wouldn't have gone blind but he couldn't have been spamming techniques like how Sasuke does. He would have to conserve, because we know Hashirama would have had high stamina, lots of chakra including some from tailed beasts, and a powerful ability to defend with wood style.
We know that amaterasu can be dodged. It can also be blocked if the user doesn't have a clear line of sight. Plus, it uses a large amount of chakra. Tsukuyomi would have been worthless, because Hashirama would be immune. Susanoo is one technique that we don't know any weaknesses for yet, but we have seen powerful attacks be able to pierce it (Raikage broke one of the ribs with a punch. Danzo pierced it with a wind bullet. Mizukage melted it with acid). If Hashirama had other powerful ranged techniques and enough chakra he could have done the same thing without falling into range of the Susanoo's attacks. We also don't know what kind of weapon Madara's Susanoo had: Did he have a sword and shield like Itachi, or did he have a ranged attack like Sasuke?
In any case, it's not unthinkable. If Hashirama had enough chakra he could definitely have won the battle. I think EMS is not as powerful as we think it is. The only person we've seen have it is Madara, and he's never used it besides his space/time jutsu. Sasuke has EMS now but we've never seen him use it and we don't know how much chakra he has. I suspect EMS is not as powerful as we think.
