One of the n0/iroh devs here.
replyIroh doesn't use DHT as its main discovery mechanism. It uses DNS/pkarr and relays as the primary method. DHT is a separate feature if folks like to do that, we don't have it on by default and don't have it on the public relays.
The whole idea is p2p but trying to be realistic about what network environments actually look like.
There has definitely been a lot of blind-idealism in a lot of P2P systems, yea. Though sometimes that's because it was/is just a PoC to see if it works at all, and then it grows too large to change / needs to be forked.
replyIroh is definitely near the top of my "play with it some time" list, that pragmatism is very important for building normal things that normal people will be using :)