The idea itself is sound, having an agreed specification allows others to build tools around this specification. (i.e. auto-generation, integration). In theory, this makes development easier. OpenAPI achieved this and is now widely used in various tools including Amazon API Gateway.
The types of diagrams you listed above are great for describing software in useful ways, but none of them are rigid enough to spec out an async API.
I still need to review this spec to fully understand it, so I'm not promoting AsyncAPI. I like the motivation behind it.
edit: typo