If your system relies on DNS, there's no decentralization; you just change whose hands your fate rests in.

Email, Mastodon, Matrix and XMPP are not decentralized. You just exchange reliance on Google / Microsoft / Proton / Fastmail for reliance on Godaddy / Namecheap / Porkbun (in addition to Let's Encrypt, ICAN and the registration authority).