Yes, the light is not correct because the vertex normal is not normal to the surface and since is sharing, is making an average. to inspect your mesh you can export it as FBX using FBX exporter to for example Blender. And in it inspect the vertex normal as an example: LINK
I often use youtube to search for solutions: https://www.youtube.com/results?search_query=unity+c#+cube+mesh
Maybe useful
