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.
Who? where? If they don’t like Deng I’ll show them Tito.
I don’t think a mixed economy is necessary but it sure was a good move for China in its time and place. I think that is the most important lesson to take from Deng. There is no answer that is always right. Each situation requires its own analysis.