Well even if it is broken, Gaara is not completely defenseless. not saying his ultimate defense is impenetrable, but just getting past the first wall would never mean he is completely defeatedLightining is able to break through Gaara's sand, as we seen
Kakashi activates Sharingan -> uses Zabuza's Hidden Mist jutsu -> Opens a Gate or two -> Uses Lightning Blade [which pierces through Gaara's sand]
Just an Example
But I still agree that Gaara would win