Radical economic egalitarianism implies a (strong) governmental system. If capital can be sold/transferred, capitalism (i.e. concentrated control of the means of production) will naturally recur. If capital cannot be sold/transferred, someone has to decide how it's distributed, and the only body that can do that is a (governmental) central planning authority. That gives the government enormous power, whether it's a dictatorship or not.
> You can have a dictatorial communist system. You can have a democratic communist system.
This is unrelated to what I wrote. The US is essentially an oligopoly, but it's also a democratic republic.
A governmental system is affected by the dynamics of the economic system. After many generations, the governmental system may be utterly different from what was originally established or intended (as is the case in the US).