PBR materials deal with more maps, a diffuse+specualar workflow will look good in certain settings. a pbr material will make the material look correct in all lighting. most maps inside a pbr material go as followed, (albedo,normal,roughness,metallic) most reason why people go about the pbr method is to have accurate metals and materials represented. i see your argument that environment is a huge factor on the way a materiel is displayed and yes you can achieve a good result with diffuse + specular but if you had real time lighting and lighting that changed, you will have some serious problems with the way a bike will or material will look. say you had a diffuse+spec bike and the lighting changed from day to night... during the day the you might not notice the difference in the bike but once the lighting changed you will notice the diffuse+spec version of the bike will not change. material will still look the same as the engine is not calculating the change of surface reflection like a pbr material will.
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The biggest difference between the two workflows is how the diffuse and reflectivity content is defined in the texture maps. In the specular workflow, these values are set explicitly with two unique texture maps.
The metalness workflow on the other hand, uses the albedo map to define both the diffuse and reflectivity content and the metalness map to define whether the material is an insulator or a metal. The reason for this is that metals conduct electricity, which means that most photons (which are electromagnetic waves) reflect off the surface, and any photons that pass through the surface are absorbed rather than diffused, so metals typically do not have a diffuse component. Insulators on the other hand reflect a very small amount of light (~4%) and much of the of light that hits the material diffuses or bounces around the surface creating an even distribution of color.In practice, this means that much or even all (if your texture has only metals or insulators but not both) of either the diffuse or specular map will be wasted information, so the metalness workflow is usually more efficient. However, one of the drawbacks to storing both diffuse and specular content in the same texture is artifacts along material transitions.
Gloss and roughness maps define the same information, but usually on an inverse scale. With gloss maps, bright values typically define smooth/glossy surfaces, while roughness maps typically use bright values to define rough/matte surfaces. In some regions, the word glossiness is a synonymous with reflectivity, so some people think roughness is a less confusing word to use. The important thing here is not what the map is called but what the values represent, if in doubt, talk to your technical artists or engineers.
Pros of the specular workflow
Diffusion and reflectance are set directly with two explicit inputs, which may be preferable to artists who have experience working with traditional shaders.
More control over reflectivity for insulators is provided with a full color input.
Cons of the specular workflow
Easy to use illogical reflectance values which gives inaccurate results.
Uses more texture memory than the metalness workflow.
Pros of the metalness workflow
The albedo map defines the color of the object no matter the type of material, which may be easier for artists to understand conceptually.
Simplifies materials into two categories, insulators and metals, which may make it more difficult to author content with unrealistic texture values
Uses less texture memory than full color specular workflow
Cons of the metalness workflow
Material transition points cause white line artifacts
Less control over reflectivity for insulators*
If artists do not understand workflow, it’s easy to use illogical values in metalness map and break the system
hopefully this clears up some misconceptions, yes you can achieve the same results going both methods but imo pbr is still the way to go