Maybe this may sound crazy but maybe; Hiruzen was able to beat two Hokages at the same time, and both, the First and the Second were just Killing machines with no consious whatsoever, just to destroy their objective, this being said, Hiruzen beat both of them, and this means and even was stated in the manga itself, Hiruzen was stronger than the first two Hokages before him, now Hiruzen would never beat Madara, yet the First was stronger than Madara, and problably this means that Hashirama was the only shinobi able to fight Madara, like the saying that goes, "it was a job that could be accomplished by just one person", makes sense? I'm not saying that the first was not strong or he is weak, that has been stated and proved maybe, Hashirama was a complete badass, also Madara, but the Third was stronger than the First and the Third would not beat Madara, only the First, and once again is was a job that only one man could do because of his skills. I hope you guys find this rasonable and that makes sense :shrug: