DNS isn't decentralised it's more federated. I believe Iroh has the option to use DHT here, last I looked at least.

Exactly. We use DNS TXT records for our default address lookup system. But we also support fully p2p address lookup via the mainline DHT.

And if you have another suitable system, you can also plug it in. E.g. you might want to use another DHT that allows mapping from a key to some address data.