The Susanno's that was weakend by physical attacks were not complete Susanoo's...we never seen a complete susanoo damaged by a physical attack... I guess we're about to find out that Madara is using his complete Susanoo...when Sasuke's was complete we didnt get to see it in action because he ran out of chakra and Itachi's was not damaged again because sasuke was out of chakra
LOL, it was not weakened when A and Tsunade smashed Madara's Susanoo. Also, keep in mind:
Complete Kyuubi is superior, larger and heavier than Itachi's complete Susanoo.
Yes, Hiruzen pushed away Complete Kurama from the village, that alone would destroy Itachi's Complete Susanoo and his skull.