A planned economy has been tried. However, even after removing all market mechanisms, corruption amongst the party managed to shatter the union.
As much as Deng is hated, he managed to set the foundation of a mixed economy, which, as we can see by the great growth of China, was probably the correct thing to do.
Later adaptations by the CCP managed to incorporate precautions to prevent internal corruptions, and furthermore, bourgeoisie corruption to avoid the dissolution of China and shock therapy.
Furthermore, after the dissolution of the USSR, many communist parties followed China in pursue of a mixed economy, leading to growth and the betterment of society as a whole.
That’s not to say that China doesn’t have its flaws. Particularly in its neutrality and lack of action internationally.
The extent depends on the existing level of development. If there is already a large and developed industrial base, then it may make more sense to go with a more heavily planned economy than one that also implements market forces. Further, it wasn’t strictly necessary in China’s case, merely the correct choice to make in the given circumstances, but certainly not a hard requirement. The DPRK grew 3.7% last year as estimated by the ROK despite being overwhelmingly publicly owned and planned, and under intense sanctions. Moreover, even under Mao and later the Gang of Four, there were still markets and private property. Economic growth and development was still positive pre-Deng, just unstable:
You’ll find that those of us on Lemmygrad are generally supportive of Deng Xiaoping, Socialism With Chinese Characteristics, and Reform and Opening Up. Deng Xiaoping Theory correctly applied Marxism-Leninism to the conditions of China, and as such appears to have paid off extremely well. I would say this was the correct course of action, as would most here.
Secondly, I think it’s important to understand that all economies are mixed forms of ownership, with the exception of tribal communalism and eventually late-stage communism. Even the DPRK has special economic zones like Rason. Socialism is not defined by its purity, but just like all other modes of production, by its principle aspect. In the PRC, public ownership governs the large firms and key industries, while diverse forms of ownership exist in the medium and small firms, such as private, joint-stock, cooperative, and sole-proprietorships. By controlling the key industries and large firms, the CPC and the working class as a whole has the real power in the economy, the one who controls the rubber controls the rubber ball factory.
Over time, this form of ownership changes. Public ownership becomes economically compelled as firms grow in scale, and class conflict rises. Not everyone will chart the same course China has, because not everyone will come from the same semi-feudal, post-colonial background. The west will have a very different approach, most likely, as will countries in South America and Africa, Southeast Asia, etc. This is why the CPC calls their model “Socialism With Chinese Characteristics,” in anticipation of “Socialism With Mexican Characteristics,” “Socialism With Kenyan Characteristics,” etc.
One final thing, I recommend looking at Cheng Enfu’s model of the “stages of socialism.” This best helps contextualize the course China is taking, and where they are at in this course. The PRC is currently in the “primary stage” of socialism, which is why they have the structure they presently do. Over time, they are developing more and more, allowing them to advance to higher stages of socialism.
By becoming an alternative to the US Empire, the PRC is positioning itself to better help those that also cross the river and join their comrades in building socialism without fear of being isolated. China is playing a major role in fighting imperialism through multilateral development, which is essential at this point in time for the global south to be liberated from the global north.
Hope this helps!