I do not understand how they do to import warcraft reforged with functional texture orm etc.
As far as I learn these textures are call pbr textures,combine with lighting,sharders it make model look more real,pbr textures has a lot of textures( height, normal , ambient occlusion, roughness, metalic) but in reforged only use normal and orm ( orm include ambient occlusion,roughness, metalic), diffuse is like a normal texture in classic, emissive make the model more glow( you can see where it glow in my custom kiljaeden texture emissive).
Normal texture used for faking the light of bumps and dents in model
Ambient occlusion used for used to calculate how exposed each point in a scene is to ambient lighting
Roughness control the sharpness of reflection
Metalic tell the renderer what part of a surface is treated as a metal and what part is treated as non-metal
Conclusion, pbr textures make model look more real, natural,fast render and can use in modern engine.