On my phone, i'll say more later, but you only show diffuse and normal content in your breakdowns. Where's your metalness, Gloss/Roughness, AO? Also technically the color content for pbr engines is referred to as Albedo, not diffuse.
Concerning material definition: An instructor of mine once told me that you should be able to read a material without a diffuse. For most materials all you need is a good normal map, specular and gloss texture. A nice diffuse then serves as the cherry on top. That's of course with the current gen workflow, not the PBR…
Sure. Ask yourself if you can look at the material by itself, without the context of the models/scene and be able to read what it is made out of? Its difficult to define clean materials. The temptation is to leave it plain. Preferring clean environments is fine, but even the cleanest things in real life have variation. Do…