People can be on the same general level without operating in the same sphere. Kabuto was considered to be on Kakashi's level because of his skills and the dangerosity of his medical ninjutsu.
Not to mention Jiraya and Orochimaru were basing their facts on what they actually knew from Kakashi, which means since the period they left the village around 12years before when Kakashi was 15(roughly) since they had actually no way to know part1 Kakashi's level without having being in the village for that long. Orochimaru himself who mentioned it was surprised Kakashi could use fuinjutsus when he sealed his Curse Seal, showing that Kakashi's true potential was unknown by him
Furthermore on Kakashi's own admission, he was out of shape in part1 because he laid-back a lot, not going in dangerous missions in the past years while enjoying peace to the point he needed to open the first gate just to complete a cliff-climbing that he easily used to complete just as a warm-up