I disagree with the premise that it failed. It advanced the socialist holdings around the world, then fell.
If China falls, it does so without advancing anything.
Surely you can see where my thinking is with this. A more hollistic view of the whole period of transition to socialism will show it as expansion and contraction and expansion and contraction. The USSR expansion and advancement of socialism will have actually achieved something, should it fall China's will not, it will be wasted.