Well, reports are reports. From what I saw, when owning them, The 8x40 Nikon AE were really bad off axis and enough to be overly distracting. The 10x50's are a bit foggy in my memory of off axis sharpness performance, so I cannot really say if they were as bad. Sure there are many other things to look for in any binocular, but the off axis was so bad in the 8x40's, I rejected them.
Bottom line here is, you are happy with yours, others are happy with theirs, but I returned mine and ordered a pair of 10x42 Nikon Prostaff 7s, which to my eyes are a whole lot better in other regards, such as weight, and off axis sharpness.
From what I have read, the 12x50 and the 7x35 Nikone AE have field flatteners in them, which is probably why they are better then the rest of the AE line. I'd still like to try out the 12x50 Nikon AE to see if they are sharper than the 10x50's. But alas, I have no access to a pair to try them out.
It sounds like you got a terrible sample.
Not aware of the outer field being ‘unusable’, what is it you are trying to see in the outer field?
Also surprised you are so impressed with the Prostaff 7’s, the AE on axis sharpness is vastly superior. .