It's easy to get good results with capital from capitalist system and throw it into welfare. But you are taking about communism as a core system.
We don't see good examples of it because it fails incredibly fast, and then leaders who tried to build communism understand it, but aren't willing to acknowledge mistake because they will lose power. Thus, they continue to build autocracy.
If communism as economic system works, we first need to prove it as successful PLC of a smaller scale, such as a company that produces something being fully community led from the inside using communist principles, and for such company to be able to compete on the market.
Still multitudes better than soviet union at any time and period.