I don't think Shin is going to win this.
Houken is like the ultimate Antagonist, if Shin overcomes him, then no fight from here on out will have quite the same stakes. Sure you can make excuses that his Friends weakened him, but at the end of the Day Shin beat Houken.
I think what will happen is that Houken wins the Duel, but then the rest of the Army just piles on and on until Houken is finally death, proving that at the end of the Day Houken did not transcend Humanity.