The 9tails foreshadowed Sasuke's power and compared it to Madara's. I think this is why the 9tails kinda feels that Naruto would lose to Sasuke if they were ever to fight again in a way. He also claims that Madara's power are even more sinister and powerful then his own. So we go back to what Madara said about his perfect Susanoo and it being able to crush tailed beast is probably true.
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