I pointed out last chapter that it was ridiculous for Kabuto to stand against the Uchiha brothers, but with this reveal it does make sense. Sage Mode + Snake Buddies + the fact that they can't shoot to kill makes it very difficult for them to defeat him, despite the fact that he has no chance of taking both of them out. Itachi should be pretty good at beating people without killing them, though, considering how long he had to fake being the bad guy.