I’m not an expert in this, but i think the best way to replicate that look would be to by scattering mesh fibers, or maybe using hair. I don’t think you can get satisfactory results with a single plane object and displacement. And certainly, mapping the roughness is not correct way to do this either. Maybe sheen, or anisotropy, but not roughness.
Its not reflection you are seeing in your reference photo, its just the fibers catching light in another direction, to simulate this you could just mask a lighter color on the diffuse, dont use reflection for carpets