sorry about the dubble post an that but this is bullsh*t like itachi said to little sasuke dont kill the piggy jus cature it lol the piggy being kabuto if it was a kill mission you would have seen the complete evapouration of kabuto end of
It's true that itachi doesn't want to kill kabuto,the same thing to kabuto but sasuke still intend to kill him. Even then, when they both arent trying to kill each other, kabuto had the upperhand, and because of that itachi couldnt even lay a hand on him. That's why sasuke helped him with his intent on killing while itachi just needs to buy time to activate izanami. Kabuto keep on beating itachi, but he came back cause of edo.
Even though kabuto attacked more than itachi and sasuke does (without his intent on killing), it matters how long can they sustain the battles until sasuke run out of chakaras, and how long can itachi can withstand his techniques. It's like kabuto playing with them, and it looks as if two brothers are really trying hard without killing him. Like I said, Kabuto has limitless chakaras, and he can can attack as much as he wants to.