Now let me start off by saying i have no problem with naruto being rusty as its been years since he last battled anyone of note worthy power. what i have a problem with is that he was so easily pierced
when naruto fought Orochimaru
orochimaru's sword of kusanagi couldn't pierce naruto in his four tails form the sword of kusanagi is said to be so sharp it can cut almost anything and will still hurt you no matter how hard your body is.
so wouldn't it stand to reason that naruto in his kyuubi cloak would be far more durable than he would be in his four tails form so logically speaking shin's sword should not have been able to do one iota of damage to him