Is harmony subjective? Probably. The thing is to recognize it when it happens. If it's harmonious just for you, then so be it. In this image, the bands connecting the sides of the frame also partially reflect the little island and give three dimensionality to it. The human in the shot gives scale, which often is missing in landscape. Sometimes ambiguity of size is wanted, but sometimes what appears imposing in person is not when it's trapped inside of a frame. Scale is an important element of context.