Stackful vs stackless, that's the big difference and the point of the original comment. Stackful abstractions are strictly more powerful of stackless ones (go coroutines subsume async/await but not viceversa).

You can have good ergonomics and performance with stackful cooperatively scheduled tasks instead of a stackless sync/await abstraction.

Async/await makes sense when you have so many tasks that you cant afford to dedicate a full stack to each of them and segmented stacks or heap allocated frames are not an option (for performance or compatibility).