Curtis talks about this in his farewell letter
https://urbit.org/posts/essays/a-founders-farewell/#urbit--a...
>Urbit's distribution and sponsorship hierarchy of galaxies, stars and planets is not designed as a political structure, or even a social structure.
>Socially and politically, Urbit is a flat network of planets.
>The sponsorship hierarchy and the senate of galaxies ... are technical governance mechanisms. ... Because sponsorship has an escape mechanism, it is not a feudal bond
AFAICT the hierarchical part (with Azimuth) is essentially just for routing packets while the application layer stuff like chat is effectively peer-to-peer.