I don´t think sim is unrealistic in terms of viewdistance. It could be improved for sure, but it reproduces it quite well. But it´s entirely depending on clouds and sun positions basically, because fog is also a cloud layer in game. Clouds block light and objects (not all to be honest as some still appear as black distant shapes) depending on their thickness and also generate shadows according to their shape. When you have fog on a valley you can clearly see its progressive effect on the mountains sides.
But even with that implementation live weather can also generate low visibility with almost clear skies if there is a very thin fog layer as the one you can find at some beach areas. I flew yesterday over California and that thin grey layer was generated resulting in a quite realistic low visibility with clear sky environment. If that layer is not just at your current location but some miles ahead of you then you can have that typical hot summer humid aspect in game. All depends on the live data and how seamless it is depending on the nearby live sources they use.
About the darkness of image using HDR and removing all postprocessing effects together with a proper tunning of contrast and brighness helps a lot to have an overall much clearer environment, even at sunset with cloudy weather. Postprocessing is degrading image a lot in game in my opinion.
Cheers