No one is pretending services will discover and configure themselves. This is just nice documentation.
You could also do some really horrific things with XML. YAML isn't amazing but its its a lot more plain. Parsers seems a lot more stable these days because of that.
Yes, HTTP+Json API is not very different from SOAP. But it's not the fault of OpenAPI if everybody does them. At least OpenAPI and OpenAPI-generator fill the gaps that were missing (an IDL and contract based code generation)
You could also do some really horrific things with XML. YAML isn't amazing but its its a lot more plain. Parsers seems a lot more stable these days because of that.