Nah; people seem to misinterpret what cubemaps are actually for a whole lot and lighting is one area people seem to think they influence. Cubemaps are effectively a bunch of screenshots of your level, taken from the location of the env_cubemap, that when put together form a cube (just like a sky map in HL2). These screenshots are then used to help provide more realistic reflections, refractions, and other effects on the materials that use them.
The reason the lighting looks bad (particularly so in the second two shots) is because of a lack of shadows and contrast. It's actually almost like there are no shadows at all, though that is probably because the angle of the shots and the angle of the light_environment aren't too complimentary. Maybe get some alternate light sources in there to help provide contrast, play with the light_environment angle to get nicer shadow placement, and tweak its brightness/colour to make things more interesting ![]()