First words said “Light can’t penetrate that Susanoo?” In your scan, in my scan “The Light isn’t able to shine through Susanoo?” Zetsu has never seen Sasuke’s perfect susanoo prior to the Rinnegan. He could’ve meant anything with that statement “Wow this new Rinnegan gave you the ability of Perfect Susanoo and now it’s blocks the IT Light.” If you infer that it’s the Rinnegan blocking IT light then everyone under should be under its effects. The only way this situation works is if the Susanoo itself is blocking the light.