The one distinction that I think is worth making is that OpenAPI describes HTTP APIs using the semantics of HTTP. Corba and SOAP attempted to be protocol independent. That's much harder to do well. Another good aspect of OpenAPI is that most people who are using it, are starting towards using the definition as the primary design artifact and then letting tooling work on that. Almost no-one designed WSDL or IDL by hand. Focusing on an OpenAPI as a design contract helps developers produce solutions that are more independent of tooling. And that's a good thing.