You two are expecting a lot of the lens! It's not that bad but not quite up to the sensor.
Right - the DA 18-135 is a good, but not great, lens. It's only a ~$400 lens on a $1300 camera!
Actually the old K28/3.5 MF lens, for a little over $100, would probably do much better.
Either its lens not focus or the image processing is too destructive to destroy the finest detail of image out of JPEG.
Should be sharper.