Who said that? Orochimaru, one who has been far from the village from a long, long time; so he couldn't know anything about Kakashi's strength level in that moment too, except make an extimate that he was strong but not as strong as him. And Jiraiya, and here that's the same with Kakashi, but also he didn't know anything about Kabuto. Also, if you compare part 1 Kakashi's feats and part 1 Kabuto's feats, Kakashi rapes him. He is faster, has better reflexes, is physically stronger, has better taijutsu, better genjutsu, better ninjutsu. Not to mention that in two times, one time Kabuto, even with favourable circumstances (
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) prepared the hell out just to escape from Kakashi, who didn't even uncover his Sharingan and still stomped him; another one Kakashi showed great confidence and willingness to fight him, while Kabuto... pretty much run away (
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). And remember that Kabuto was the one willing to fight Jiraiya and that was joking without even being serious and having real killing intent against Tsunade, and the same that of course (verbally) challenged part 1 Kakashi. So a cocky one, for sure.
On topic, I'd say that I can see a slightly advantage for Kabuto.