true about the kamui shuriken, but not true about the chakra arms being slapped away. Sure naruto and minato initially slapped them away, but the giant rasengan ate through them, forcing obito to use his TSB shield to defend against it.
Why can't the real one phase if kakashi warps a clone there? Obito has warped many people into kamui zone and proceeded to warp there. If juubito can negate the effect of kamui warp, then kakashi negates juubito's kamui warp.
Can't kakashi's PS just dodge the juubidama? his PS has shown increadible speed, and it can fly, getting hit by the juubidama isn't happening without a distraction or restricted movements. Even if he gets hit, it would take a ton of juubidamas to destroy his PS if it's as durable as Sasuke's one.