ChiSao covers a whole hell of a lot more than 'parry techniques'. It covers applications of most of the core WCK methods, tools and tactics in an alive dynamic fluid framework against resistance.
Any stand alone technique drill is what we call SunSao, a part of the whole without continuity and flow, it is dead.. ChiSao (poon sao) while limited is alive training, of the core WCK elements and method. It is not the first drill, nor the last.