He is clearly not as strong as Naruto. That is unless his EMS ability is just plain epic. Kishi showed us a little of what Sasuke is now capable, but from what we saw in Obito's hideout and against Kabuto, Sasuke is little more than fodder at this point. He still had the weakest form of Susanoo, his Amaterasu seemed weak when compared to Itachi's, and he still only used the basic Sharingan genjutsu.
However, Sasuke could have some epic new EMS ability that hasn't ever been seen before. His eyes could be so powerful now, that he impresses Madara in this battle and gets to learn some new Sharingan/Rinnegan secrets. Sasuke also spent time with Itachi. We don't really know how much time passed after Itachi put Kabuto under Izanami. He also fought against Danzo who was spamming the crap out of Izanagi, and in both battles, Sasuke had his Sharingan active. Maybe he now knows how to use the two Uchiha forbidden techniques. Maybe an EMS is not bound by the same rules for using Izanami and Izanagi.
I could see Madara completely massacring the entire shinobi alliance, or just Team 7, at which time Sasuke reveals that he has just used Izanagi to reverse the effects. As Madara gloats over his victory, the events replay, and it is revealed that right before the attack landed, Sasuke used his other eye to trap Madara in Izanami. The Hokage explains the sacrifice that Sasuke has just made in saving everybody and trapping Madara, and everybody acknowledges that Sasuke just gave up his most prized possession (his eyes). However, instead of going blind, Sasuke doesn't lose his sight, or even more surprising, Sasuke awakens the Rinnegan.
On a side note, I still don't know where the idea that Naruto doesn't have access to all of Kurama's came from, but Minato only sealed half of his chakra in order to weaken him for the sealing process. He sealed the yin chakra in himself because Kurama's yin chakra was based on hatred, bloodlust, and destruction. If he had only removed the yang chakra, Kurama probably would have still been too powerful for the seal to hold. Kurama's chakra has since recovered, and Naruto has had full access to it since they started fighting Madara.