GNUnet is more of an attempt to replace the entire internet, with replacements for every feature of the modern web, while Reticulum is a far more solarpunk and permacomputing vision. It’s a very practical, implementation-first approach.
It’s primarily a cheap, easy, practical tool for a local community, which can be linked with other communities around the world using any means practical.
That’s the dream. However that really only exists in local areas. Good luck trying to get companies to host on a radio mesh network.