Yawn,
I guess that Lloyd got a bad lens, as I have no issues with the Q2 and corner sharpness. Excellent optic for a 28mm lens. Sure wide open you can see a bit of corner sharpness, but by F 4 even 3.2 corners are fine, at least from the images I have taken with the camera.
Can't speak to how same lens will work on the Q3 with the increased resolution. However I can state I found that the Sony 61MP sensor was not as great a step up in overall DR as I had hoped, having used it extensively in the Sigma FP-L.
Paul