This is a very loaded claim that you have not provided enough evidence to prove. Socialism and capitalism are very new economic systems, and we don't know if one is better or worse with productivity (a word also poorly defined here).
Also, the "spoils" of capitalism have arguably always been distributed badly, and built on the exploitation of millions of people. We aren't living in a unique moment in time. A lot of capitalist wealth was initially created through slavery and that still happens today.