Unfortunately I have to agree with this, a relay sits behind a url. However, you cannot argue Nostr is not decentralized due to relays, take a relay down others will be setup, you cannot stop the sharing of information by taking down relays.
As long as the data that is made is independent of a domain, it’s not centralised and can flow and be accessible anywhere. When data is only accessible from single point, it is centralised. Web5 DWNs can also be considered “centralised” if everyone use a single central cloud provider, but both protocols support any number of relays/DWNs pr user. There is no chance that Nostr and DWN is going the way of Telegram/Samorai.