Kimimaro Kaguya a merely low-level jounin?
Let's make a review of the fights he has has:
First of all , he took on a young Naruto by himself. To be more precise, he took on at least 100 Narutos(He used the shadow clone jutsu) and single-handedly defeated each one of them with little effort, if any effort at all. Furthermore , Naruto was enraged due to the fact he wasn't able to lay a single finger on him and thus started to use the nine-tails chakra but it still was pointless - there was too much of a gap between them.
He almost killed Naruto without receiving a scratch on his body , that should say something.
After fighting Naruto , he took on Rock lee , who had just recovered from his injury. Yes , it's true that he was officially just a genin but unofficially he was a Jounin-level ninja , in my opinion. With the use of gates , he was literally unbeatable but even without them , his power was still superior to the average shinobi. Kimimaro did not only took on Naruto but also Rock Lee, a taijutsu master , in a taijutsu fight. That alone should speak of Kimimaro's prowess in taijutsu. Note that Rock lee even got drunk(In this state it's said that he could only be stopped by Gai,Neji and tenten at the same time) and still didn't do much damage to Kimimaro, who still had many trumps cards left.
Finally , he took on Gaara , the man who would be later known as the Kazekage of Sunagakure, a frightening man indeed. Gaara managed to put Kimimaro in tight situations , but was never able to take the upper-hand in the battle at all. Take note we're talking about a Jinchuuriki that was able to kill you in matter of seconds if you were in close range but Kimimaro still managed to defend himself, let alone attack.
Kimimaro fought three amazing ninjas and didn't lost any of his battles.Furthermore , he was never killed and would have killed Gaara and Rock lee had it not been for his illness.Yes, this was all when he could barely move his body and was only fighting due to his unstoppable will.After taking this into account, we're talking about a S-class shinobi who would present a threat to everyone.