Static or dynamic palpation is an art. It's perception and interpretation are purely subjective. Diagnosis is based on inductive and deductive scientific principles. However, percussion is an art. Auscultation is an art.
Observation is an art.
Questioning is an art. Listening is an art. To say that dynamic palpation to sense joint fixation is unreliable because of examiner variables is missing the point. For example, imagine six of the finest artists in history painting the same scene. Will the resulting picture on their respective canvases be the same.