I see now, I misunderstood your original post. You were saying async/await is necessary because futures work badly, not because all the alternatives (i.e. locks) work badly.

Sorry, my mistake!

Edit to add: futures work badly in every language, so there's no shame in the borrow checker not working with them.

Edit 2: But in that case we're back to "why would Rust want async/await over (potentially green) threads with its first-class support for locks?"

I believe these are the talks from Steve that he's referring to. It was enlightening for me:

1. Rust's Journey to Async/Await - https://www.youtube.com/watch?v=lJ3NC-R3gSI

2. The Talk You've been Await-ing for - https://www.youtube.com/watch?v=NNwK5ZPAJCk

The first video goes into all the bits you're concerned about and all the things that Rust has tried before arriving where they are now

Language support for green threads require a heavier runtime (so you'd pay the performance cost even when you didn't write async code).

Tokio basically is green threads as a library.

Regarding your edit 2, I linked two talks I have that go over this in great detail elsewhere in this thread.