Gemini and the web are both decentralized protocols, and it's silly to say they aren't. You don't have to be p2p distributed to be decentralized. Centralization for both happens at a higher level, when people make themselves dependent on certain sites; in particular, when they use social media platforms rather than (fungible) hosting platforms.
If you want to self-host without dealing with DNS, VPS, or static IP, run Gemini as a TOR hidden service. That'll even let you host your lolicon shit, if you're a filthy pedo. Just... don't expect anyone to link to your gemlog.