I don't know where the notion about Darui and Kitsuchi being on PTS Kakashi's level comes from, but for Kabuto, it's simply not true.
Yes, he was hyped to be that strong, but the fact of the matter is Kabuto with a hostage was stomped by non-Sharingan Kakashi.
His only achievement was running the f**k away from him.
Manga facts > hype in case they contradict.
Oh no, I might have just awakened the devil. xd
Also, Zabuza was not on Kakashi's level, too.
Kakashi himself stated that he had underestimated Zabuza, that's the reason he landed in the Water Prison (which, mind me, would only allow Zabuza to kill Tazuna without resistance, to kill Kakashi he'd need to release him). Following this statement, Zabuza began to take a harsh beating from Kakashi, both in the forest and later on the bridge.