Well, in the danzo fight, he seems to be getting more and more drained as he is spamming arrows. You forget, if raikage starts out like he did the first time, he has four limbs, plus he gets several hits in before sasuke uses susanoo. If it comes to another scenario where gaara, his bodyguards, and darui come in, they get that huge attack in, which could possible weaken susanoo enough for raikage to penetrate. Plus, who said it even gets to susanoo? Maybe sasuke's long hair gets in the way when he uses amaterasu and burns him to death, and you forget gaara's sand coffin attack