you have no proof SM makes his actual chakra more durable. also his chakra has nothing to resist the cut of the sword. It has no bones or structure like susanoo. the reason it tanked the bijudama is because it wasn't a piercing attack. Can you pierce a mattress better with a hammer or a sword?I dont really think that Sasuke could just cut through chakra tails strenghtened with natural energy. BM Naruto dosplayed some insane tanking feats, with SM its only brought to the next level.