Well, I wouldn't put it like that. Async can trivially cash out into parallel work like if you're just sending queries to a database or ffmpeg or ImageMagick or

Well, I wouldn't put it like that. Async can trivially cash out into parallel work like if you're just sending queries to a database or ffmpeg or ImageMagick or, frankly, most common use cases which are going to do work in parallel out of process. All of your I/O work could even be happening in parallel in a run of the mill JS app. Workers just give you parallelism with your sync JS code which is a more narrow claim.