I wish it had support for a system similar to webrtc's offer and answer SDP messages.

From what I see, relay servers are doing a job that is equivalent to Stun + Turn + SignalingServer in WebRTC.

This is great for simplicity, but having Stun Turn and Signaling live in the same server would make it harder to secure. For example, since in webrtc signaling is up to the user, it is most common to have signaling implemented as a web server, this allows you to have it behind cloudflare with the signaling server ip never exposed to the internet. If you are not interested in supporting turn, there is plenty of public Stun servers that can be used and Stun itself is a really cheap server to run.

For iroh, it seems if I wanted to self host relay servers I'd be forced to expose their IP to the web which would make them really expensive to run if one wanted to make them DDoS proof.