Exactly, so it does tell us that CM-400 is not comparable to a Supersonic cruise missile since it reaches high speeds only in the terminal stage. That's why China might went for P800 version, to get similar performance in similar roles, otherwise there would be no need for this.
That would imply that they wouldn't spend billions into weapon development and reseach, but that isn't the case. Their defence spending is very high too, only the production costs are low and the development pace extreemly fast. But is it really a choice they took or is it a necessity? China has very limited options of technological cooperation and that is limiting their R&D too. Why does a nation with this industrial and finacial potential need to copy designs, if they could develop own alone?
It's one thing to develop something from scratch based on specific requirements and development goals and it's another to copy designs to just for the sake of having a similar weapon or aircraft. China might be no 1 in the world when it comes to industrial capability, but in R&D they still lack behind, although I have no doubt that they will catch up faster than many believe.