Issues with using texture maps to represent reflections in architecture

Questions
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1

The principle of roughness and metalness maps in THREE.JS is: the roughness map determines the smoothness of the surface, where black represents a smoother surface and white represents a rougher surface. The metalness map determines the amount of metal in the surface, where black represents a non-metallic surface and white represents a metallic surface.

I followed this principle to create my maps, but I found that the grayscale values for roughness and metalness did not show much difference. Only when the grayscale values are either completely black or white, can I see some variation in material texture.

Thank you

1
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This image is a metalness map.

2
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This image is a roughness map.

3
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2

It’s common that metalness is either 0 or 1. Values in between tend to represent either transitions between the two, or perhaps a rusted or dusty surface.

Roughness values between 0 and 1 are quite common, though.

Example: