Honestly speaking, I'm quite surprised by the result you've got on this lens. I do know that it is a Kit lens... but still !
On D7000, I noticed that the sharpness is very bad at 18 mm no matter the aperture used. The lens is then quite all right in the other focal distance. (I know it is not a 70-200 2.8) Here you are saying that it is very bad pretty much everywhere except at 18 mm .
That is wrong, definitely !
I think that for this test, there has been a lack of serious.