On your sample photo, fog or smoke in the air seems to be the reason why further landscape is not sharp. Nothing in your camera can help against that. Try coming back at another time to see if the air is more clear. Above a city with polluted air, this might never happen.
A wider aperture with faster shutter time will result in equivalent exposure, but depth of field will be smaller, because it is determined only by the large aperture. Opening up all the way is bad for sharpness because most lenses are getting sharper when aperture is smaller than maximum by a stop or two (unless you hit diffraction limit).
To get maximum depth of field, you should focus to something far away to ensure that you are covering hyperfocal distance. You might also still decide to use f/8, because you might prefer even overall sharpness to better sharpness at smaller range. In technical side of photography, compromises have to be made quite often.
Another thing you could try is sharpening in post processing (e.g. using Unsharp mask).