I do not see this a valid argument due to lack of premise.
The fact that China is the 2nd largest economy is an undeniable achievement that even you agrees.
For the reasons of that, your explanation has some point in it, but is not complete, there are so many countries, why other counties start from same poverty level did not develop so fast? There are other reason, the most reason is not in your answer.
I think another reason it the effect of dictatorship, that is not a propaganda, several Canadian politicians has said similar things, and there are still other reasons.
You can not prove it, because you can not change history to see if it works.
Actually, Taiwan developed very slow these years since it changed to "democracy" which is very low efficient governance.
In recent years, South Korea's development has a large portion that benefit from China. China is South Korea's largest economic partner.
North Korea's problem is not caused by China, It's their own choice.
My opinion is different with you, but I don't want to talk about Mao now, I have talked about him in the this forum.