In heavy turbulence one should try to mantain attitude not altitude.This is the reason for Boeing saying to fly with a/p in CWS and a/t disconnected.By doing this the plane will not try to mantain altitude (which will result in more abrupt manouvres in case of heavy turb) ,but will try to mantain attitude set by the pilot.
Nothing to do with dutch roll (has nothing to do with a/p or turbulence)