Beautiful sunset
Did you use an UV filter/ any other filter for this photo? And if yes - which brand/modell?
Did you check, if your AF has to be corrected for your camera or does it work at maximum sharpness with the actual settings?
We can't expect quality of a prefessional lens from a consumer lens. Of course, there will be better lenses out there than the 18-55. Read your review of the lens. I can understand that you want more from a lens - but I do not think that the 18-55 is a lens with poor IQ. Maybe you'll find a way to get sharper photos with it.
I bought the Sigma 17-70 HSM - latest version - and to be true: it's not much better than the Pentax 18-55.
Best regards
Holger