Itachi is young and strong, able to use his Mangekyou Sharingan a lot of time. Kabuto possesses the DNA of Orochimaru, Suigetsu's liquification abilities, Karin's healing powers, Jugo's ability to passively absorb natural energy, Sakon's "Attack of Twin Demons", Tayuya's Sound Based Genjutsu, Kidomaru's Web Attacks, Jirobo's Earth Release techniques and Kimimaro's Kekkie Genkai. Now it might seem that Kabuto has been made too powerful but if you read Manga, Kabuto possessed all these powers when he fought against Sasuke and Itachi.