Greed attempts to attain maximal reward, but this does not mean the reward is achieved. Greed is neither necessary or sufficient to achieve extraordinary outcomes.
Rational greed exploits whatever system you have though. A rationally greedy capitalist will do startups or work on Wall Street or something; a rationally greedy communist will gain political power. In a world of magical egalitarianism rational greed will increase the size of the pie for everyone; if you allow society to break egalitarianism purely to incentivize this kind of behavior you have become John Rawls.
Greed attempts to attain maximal reward, but this does not mean the reward is achieved. Greed is neither necessary or sufficient to achieve extraordinary outcomes.