Why do you say that? It does not follow. These billionaires have their wealth for two primary reasons.

1. Investments in goods and services others value
2. Political connections allowing them to stifle competition and receive subsidies

The first is economic productivity, and the economy is a not a zero-sum game. Looking at just the monetary side of market transactions ignores half of the process, though, and voluntary exchanges are mutually beneficial. The second is political plunder antithetical to the free market. The latter might constitute "hoarding," but your assertion is that wealth alone is evidence of... something.