Should I really use specular map or leave it at default 0.5 value?

[Arkiras]

@Haoris

Composite texture is not really helping here.

The composite texture attempts to store the lost normal map detail in the roughness texture.

From the composite texture documentation:

maintains the specular size for a Material whose normal map is detailed when near to the camera, but uses the mip maps of the normalmap that might appear flat when farther away.