The Sage was a strong Shinobi indeed, however he was only a monk, he taught and preeched Ninjutsu to those who didn't believe in it. I don't believe the Sage was this.. "GODLY OMFG OP" Shinobi as everyone makes him out to be, I just think his mastery over Ninjutsu, his godly weapons, his sealing techniques, and the Juubi encounter are what made him to be so famous as he is in the NB, NV, or any Forum today.
I believe the SO6P was weak in Taijutsu, he was only strong with his weapons and his amazing mastery over the use of chakra, which would explain the jutsu Banbutsu Sōzō(Creation of all things) which forms the basis of Yin chakra to create physical forms from nothingness. Then, through the application of vitality, and the physical energy which forms the basis of Yang chakra.
SO6P was a God because of what he did, I don't think he was as strong as people says he was, he was a monk, someone that created life, with Ninjutsu, perhaps I'm wrong and maybe the So6P is some godly Ninja who can take down Naruto in Kurama mode with one finger and on his knees, but still, I think So6P is only strong with Ninjutsu, and he was never shown using any elemental styles, only sealing and Yin/Yang release.
OT: I think the Shinobi alliance has a huge boost of a chance now, no need to doubt that. They've got Hashirama, who took down Madara at his full strength, and took down the Kyuubi at the same time. They also got Tobirama, who created Edo Tensei, he's got to know some secret on how to kill an Edo besides sealing it, if their is a way, but Tobirama was brought back for a purpose besides this one.
3rd Hokage, he took down Tobirama and Hashirama at the same time, even if they were at full power or not, you cannot say that is not some beast reputation there; people loved the 3rd Hokage, he sacrificed his life to take down Orochimaru, even though he failed, I think he sure went down with one hell of a fight.
Minato, he knows much sealing techniques, and reminds me of Hashirama for some reason. He sealed a Bijuu bomb from the Kyuubi! Barely anyone in the entire Narutoverse can even come close to doing such a thing! Minato even took down Obito, which everyone has failed miserably to do, you cannot tell me that this won't be a big help, you're also forgetting this is the "Konoha's Yellow Flash" we're talking about, noted for his speed, he could dodge a full power punch from Ao, which takes a lot of speed, and I mean a lot of freakin speed.
So tell me, how are these 4 not gonna help again? All of them know sealing jutsu, we don't know if they can combine their seals to form one strong ass powerful seal to seal the Juubi back up again, the plot is still running forward, it could happen; only time will tell.