The point is that other solutions were able to use traditional threads or green threads (via stack switching) to solve the same problem without the compiler hav

The point is that other solutions were able to use traditional threads or green threads (via stack switching) to solve the same problem without the compiler having to transform sequential code into a state machine under the hood (since pre-emptive threads can be suspended and continued at any time, and green threads at specific 'yield-points'). Javascript is limited by the single-threaded browser runtime, and the way that WebWorkers were bolted on later didn't help much because WebWorkers with message passing are too inflexible to implement even green-thread-style task switching. The state-machine code-transformation was indeed the only way out of this dilemma. Async/await is essentially high-level language syntax sugar and it shouldn't matter whether it is implemented via code-transformation, or with green-threads or real threads, or a combination of all those under the hood (but in reality it matters because there's a difference between 'code slices' being scheduled on the same thread or different threads when dealing with shared resources).