Going by EvilOne's logic, Kage level>>>>bunch of chunins. Even though Sakura and Neji are both jounin level, he considers the K11 in their entirety to be just a bunch of chunins. If being a kage means you can stomp K11, Mei destroys these two, who are only two from K11, with the lowest difficulty possible.
In all seriousness, lol at the one above me who said Katsuyu solos. There are two reasons why a water dragon will kill Katsuyu. First off, slugs thrive when the conditions within their body are acidic, water will dilute the pH inside Katsuyu so it will mess up the homeostatic conditions within the slug. If pH levels aren't kept constant, living beings die. Furthermore, the water will make Katsuyu lose its form because it will become to liquid to maintain it.
As for the match up itself, I say Neji and Sakura can take this with high difficulty. With Katsuyu's size, it can serve as a good distraction for Sakura or Neji to get up close. Neji can see through the mist and use the chakra on his body to momentarily protect himself from the effects of acid mist. Sakura can momentarily disperse the acid mist by punching the ground. If she gets close to Mei and punches the ground, the uprooted rock will impale Mei, killing her. Neji can, however, avoid it by anticipating Sakura with his Byakugan. He will be able to anticipate Mei's attacks by seeing her chakra network acting up while she prepares a jutsu.
