To whomever crosses this path,

after some investigation my mistake was actually not in the shader at all, I loaded an LDR (Low dynamic range) texture as the skybox, which created a blend irradiance map (light has less variance -> less variance in the generated texture), so the fix was to to add proper HDR support and load an HDR texture as the skybox.

results (still not perfect as the AO looks a bit wierd but certainly more "metallic" looking which was what I thought lack): result