I wouldn't say "improve upon nature" so much as "act upon nature," but there's a good point here outside of the straight photography argument. In landscape and nature photography I don't think we ever just record nature. We make choices about camera position, composition, depth of field, focal length, film type and more that all greatly affect the appearance of the photograph. Something as simple as focal length changes the entire scene by changing the perception of distance, and we use this to create the atmosphere we want. I think these are as much tools of creation as a painter's brush. And if we consider living subjects, even in natural light, we are making lighting choices that drastically change the viewing perception. So I agree that we "act upon nature," but I think "improving nature" is a bit naive and part of an older human-centered way of thinking. The "disadvantage" to art is old-school bull though.