If you have a metallic surface, it becomes completely reflective, therefore diffuse contribution of the lighting has very little effect and the material is lit entirely by reflections, whether they’re direct from dynamic lights, indirect from reflection captures, or SSR. If your Albedo for your metallic surface is below the average value of metals(180 sRGB), then you’re going to have a metal that is too dark in general regardless of lighting. The same concept applies when your roughness is low, because the surface becomes more reflective, although the specular vs diffuse contribution varies with non-metals.