Im gonna pitch in my thought on the topic since i didn't do so before, When it comes to Naruto vs Sasuke, there was no true under-dog. People who liked Naruto thought Naruto was gonna win and people who liked Sasuke thought Sasuke was gonna win, they both had equal chances of winning every battle they fought. The question is only answered when the fight is over and the victor is decided, like in VoTe 1, Sasuke won and in VoTe 2, Naruto won. However they both had equal chance to win in both battles.
And about that SM Part, Sasuke also said that he wanted Itachi's eyes so he could fight Naruto, so they both cancelled out each-others statements there.
And you act like Sasuke is the only one who people doubt, there were many who were doubtful whether Naruto would win in VoTe 2, yet he did. Deciding who's the actual underdog between these two is only going to be from personal opinion, as many thought one was going to lose while many thought the other was going to lose. In my opinion, its balanced.