The idiots who say Itachi defeated Kabuto
makes me laugh every time.
First it was Edo Itachi not just normal Itachi, that is something you should consider because Kabuto would rape normal Itachi anyday, in fact Itachi got killed twice during their fight:
So right here, Kabuto is stronger than Itachi.
Now another thing is Kabuto didn't have his Edos on his side when they fought. I would just love to see Itachi, Edo or not taking on 30+ Edo zombies. I don't see that happening, do you? That means Kabuto wasn't at full power. He would stomp him any day.