The Expanse's high-political scene is best described by the balance of powerful sovereigns, and how that changes over time. Companies have a lot of power, but that power is primarily expressed by influence in governments. A company gets mining rights from a U.N. charter by influence. Then the company expects the U.N. military to defend those mining rights. Sometimes the company influences the goverment and sometimes the goverment influences the company. The big exception to this is the O.P.A. which always tends centralize power around Tycho.
Altered Carbon also uses goverment as the primary seat of power. United Nations Envoy Corps are primarily a reskinning of Dune's Sardaukar, the powerful super soldiers that enforce the rule of law out of fear. There are very powerful corporations, especially those discussed in the first book, but their power is again through the influence of government, and goverment has the authority to act independently.
This is in comparison to a true mega-corp like Final Fantasy 7's Shinra Corporation, where all power exists within the company. Shinra can destroy 1/8th of the capitol city with no repercussions, and there is no significant economic activity outside of the company.