What were the material differences such that the USSR was able to use central planning to develop their economy into a superpower, while the Chinese economy struggled to alleviate poverty without seeking foreign investment?
(I get that the question presupposes legitimacy of the Deng reforms and I am too much of an ignoramus to argue one or the other, so if you think the question is a fundamentally incorrect one I'm interested to know why too)
I'd say your speculation and opinions are based off of your own studies in that area, so it would stand on much firmer ground than any assertion I could make on the PRC's economic history.