Hmmm have we even seen any chuunins do anything atall ?..

Iruka is a chuunin we dont know shit what he can do other than paying Narutos ramen and teach Mizuki got kicked by Naruto even before he got to genin. If Deamon brothers are chuunins I dont know actually.. But there are some more chuunins arround like the examiners and the two that faked the classrooms before the first chuunin exam.. correct me if Im wrong here but I cant come up with any other. Haku maby but I wouldnt count him in the chuunin ranks tho cause was probably above that in skills anyway.