You'll still get wet behind a RS fairing if the gear you wear lets water in.
However, it takes much longer to happen. Wet weather gear is still required.
1985 or thereabouts I was riding my first R100RS on a 5C night. It was a 3 hour ride and I was with a fellow on a Honda VF.
We stopped for petrol and he complained bitterly about the cold. I was almost oblivious to it, but did layer up appropriately. He was really annoyed! That was when I learned the RS fairing made a real difference.