You really think Obito couldn't have gotten that by himself?
Maybe he could have, but the point is that he didn't.
OT: Sasuke is
a deciding factor, but his selfish ideas leading to this is dumb luck. And also providing Obito with a Hachibi tentacle was a very poor decision. Not all of his selfish acts yielded good results. The decision to spare the Leaf and bring the Hokage to help the alliance was his greatest contribution, along with fighting alongside them. That was selflessness instead of selfishness; he's becoming more like Naruto.
And don't downplay Naruto's much larger involvement in the war. Without Naruto, the alliance wouldn't have made it far enough for Sasuke to decide to join them and the Hokage wouldn't have been summoned by Orochimaru to help. Though Naruto does get annoying when he whines about bringing Sasuke back to the Leaf, his whining also prompted Itachi to put the KA crow inside of him. Without Naruto's annoying behavior, Itachi doesn't stop Edo Tensei.
To summarize;
without Naruto's annoying behavior, Itachi wouldn't have put the KA crow inside of him, Edo Tensei would not have been ended, Oro wouldn't have come back, and the Hokage wouldn't have come back
If Naruto wasn't constantly talking about saving Sasuke, Sasuke wouldn't have been able to make his greatest contribution to the war.