I _think_ the reason that the comparison with OpenAPI feels weird is because OpenAPI uses one (and only one) communication interface in REST. AsyncAPI is trying to accomplish the same thing without a consensus in communication interface. This requires that any specs are far more abstract to encompass the possible options.

But consider what OpenAPI/Swagger actually changed - it made for a singular page to tell a user (or machine) all the possible ways to interact with the service and what the shape of the requests and responses would look like. AsyncAPI is meant to do the same, but it's much harder to grok with all the various protocols generalized into unnatural-looking fields/URIs/etc.