I see the lens has been returned so this is probably academic but I have done a table top test of my DA 18-55 AL WR and I can confirm what the OP is saying. The lens is very soft at the extremes of its physical parameters.
- Minimum focusing distance of 0.25 metres
- Maximum focal length of 55mm
- Maximum aperture of f5.6
With the above settings the image is virtually unusable, nothing is sharp. Stopping down the aperture to f7.1 - f8 improves matters considerably. Whilst I was not expecting great results, I was surprised by the extreme softness displayed. Despite my experience, I am not prepared to say this is an indicator of a faulty lens. I see it as an example of what happens when attempting to push the performance of a budget lens to the extreme. I would have no hesitation in recommending the DA 18-55 AL WR to anyone for general use but for extreme close up work, a dedicated macro lens has no equal.
I fear the OP will get no joy from the replacement lens.