There's some truth in what you point out. However, the effect of light level isn't just quantitative. At low light levels, the eye's perception of color changes, so the landscapes will be qualitatively different too. What's light tan at double the actual illumination on Mars could appear to be a dark umber at the correct level. A blue tinge in the air from Rayleigh scattering could take on a purplish hue at low light levels.

When I did my own experiments with landscape rendering some time ago, I tried it both ways, and decided that artificially bright was aesthetically more pleasing. But I also liked seeing the more accurate rendering to get a feel for what it might actually be like to be there. Mars in reality would be a rather dark, gloomy place...not the shining desert vistas reminiscent of Nevada that we commonly see.

Minor quibbles...those renderings are beautiful.

--Robert