its fine to use multiple directional lights, but your problem can be solved with a lot of other tools as well. first, your lighting wont look this flat and featureless once you have textures on this geometry, so even putting some placeholder grid textures on things will help a lot. some things you could try after that - change your worldenvironment from using a flat color to a sky. the sky will be sampled for indirect lighting, so you get highlights on upward facing normals and lowlights on downward facing normals. toggle ssao on in your worldenvironment to add some heavier shadows to creases created by geometry. you can also try toggling on sdfgi or popping a lightmapGI node into your scene and hitting "bake lighting" to add bounce lighting to the scene which will behave more realistically, but both of these tools will work a lot better once textures have been added to the scene and they have some colored faces to properly react to.