It's fricken obvious that they're wrong. Look at
countries by GDP per capita (basically how much the average citizen produces each year. Exclude the city-states (no rural population to drag them down), the banking countries (Luxembourg, Liechtenstein, Switzerland), tax havens, and oil exporters (Norway). The top countries are the U.S., Denmark, and Iceland at about $65k per person per year. Basically, each of their citizens on average produces the equivalent of $65k worth of stuff every year.
Most of Western Europe is around $45k - $60k. The cost of
introducing economic inefficiency to assure better income equality. Not saying there's anything wrong with this (in fact I prefer it), just that forcing the economy to do something it doesn't naturally want to do comes at a cost.
Japan, South Korea, and Taiwan are at around $30k-$40k. They suffer from ingrained corruption (winners are frequently determined by who paid the biggest bribe, not who made the best product), and cultural conservatism which makes their companies slower to react to problems and changing economic conditions.
Most of Eastern Europe is around $20k-$25k. Again, likely due to ingrained corruption. For reference, Communist East Germany was around $25k in its heyday.
Below that are the truly corrupt nations, banana republics, and economically mismanaged. Corruption, incompetence, or excess control by the wealthy result in their economies being geared towards keeping those people wealthy and in power, not maximizing everyone's productivity. Russia is at around $11.5k because the country is pretty much run to keep Putin and several organized crime bosses in power. The same goes for China - also at around $11.5k due to the top priority being keeping the Communist party in power. The Soviet Union was at around $10k-$15k as well. (The U.S. left this state when Henry Ford began paying his workers double the prevailing wage. And inadvertently discovered that if you pay workers a fair wage, the economic growth it creates more than offsets the cost of those higher wages. And he became one of the richest people on the planet because his workers were suddenly able to afford to buy the cars they were producing.)
So yeah. China's current economic state seems good to them only because they're comparing to before they introduced market reforms, when their GDP per capita was down around $1000. It's currently about 10x that, but it's still less than half what East Germany managed to achieve under Communism, and 1/5 to 1/6 where the free market western nations are at. At the very least, if they ditched Communism I would expect China to be able to match Taiwan, South Korea, and Japan at $30k-$40k. (Hong Kong is at about $50k, but that's a city-state.)