Earlier quoted context omitted.
There have been nowhere near enough actual trials of communism to conclude anything fully. The core examples were all poorer countries with various problems, corruption… To reject communism as a concept over the atrocities of Stalin et al is as reasonable as rejecting capitalism because the U.S. was built on slavery and the genocide of first peoples. The atrocities were real, and they did connect to economics, but to…
Review "The Black Book of Communism" for a catalog of the death and misery from communist countries, over and over. Voluntary communes and Kibbutzen have failed as well - none have been capable of operating without subsidy.
If you want to pick examples that point various ways, you can note that Cuba has corruption, lack of democracy, is an impoverished island suffering the effects of significant economic embargoes in the global system and yet still vies for having one of the best health care systems. They even a top country in providing doctors to serve abroad in troubled places!
And the Soviet Union was a horrendously corrupt place that failed in most respects to live up to communist ideals and yet still managed to compete technologically with the richest countries on the planet despite being economically far far far weaker in fundamentals. The U.S. only barely beat the Soviets in the space race etc while being massively richer. The Soviets had many orders of magnitude more losses in WWII also.
The history of Communism is one where anti-communists did everything they could to undermine any success, the trials were full of corruption and abuse, and even still they had notable successes.
The kibbutzen failed not strictly because all the ideas were unworkable. They failed because they had to function economically in a larger context. None of them had wealth along the lines of successful capitalists either. Capitalists have only ever operated capably by controlling a lot of capital or getting subsidy, at least in the form of law enforcement that serves the side of capital.
We can conclude that all attempts at communism so far have had serious flaws. We can also conclude that capitalism has always had serious flaws too. Anyone who takes a polarized one-sided view on this stuff can be rejected as just being dogmatic. Piketty is not one of these one-sided dogmatic people, he's actually interested in studying empirical evidence and not concluding more than the evidence can truly support.