Yeah, I remember just how nice it was going from Cooperative MT to Preemptive multi tasking -- the general view was that anything that only did Cooperative MT was just a Toy.

I'd bet that the orders of magnitude of speed from Moore's law did in CMT by making PMT doable without a huge speed hit.

Nothing I've seen from async is cleaner, easier to maintain, or better from a cognitive load POV. It's just more efficient for certain types of loads because you're being a consenting adult and not breaking things.