Hmm. I however have a different perception of all these,
1. Hokage
2. Jounins - Captains, or commanders
3. Job Levels/Chunnins - Anbu, Medics, Teachers(Thats why Naruto first teacher is a chunnin, not because he's stong or anything.)
4. Gennin - Still Require undersupervision of higher ranking ninja's.
5. Students
I view Chunnins as ninja's that are capable enough as in they act or their decision making is like adults. I'm sure most like Sasuke, Naruto, Neji, Rock Lee, and others are definitely strong enough to be Chunnin levels, but they are not chunnins, because they probably deem unfit as of yet to be in the 'proper' ninja's or the ninja working class.
And also, I don't see Chunnins under supervision of a higher ranking class. Jounins teach Gennins, Chunnins teach Students. Who teaches Chunnins?? (I doubt the Hokage has enough time to teach every single Chunnin) I don't think they have any teacher, therefore, they are like the working class of the ninjas. Some more talented at fighting, go become Anbu. More intelligent become Medics. Some more or less totally hopeless become teachers. Heheh.