>>jmakov+(OP)
I think the better way to think about async Rust is to use it when it's beneficial to developer productivity and to avoid it when not. There are quite a few situations where it makes the code easier compared to alternatives you could come up with.
I don't think for a second that async Rust should be picked for performance reasons.
You get a feeling for what is a good use of async and bad use of async relatively easily these days as the ecosystem is maturing.