I disagree with you in the last point, async is definitely painful for end users. It indeed feels like you're using a completely different language, which has Rust's core features removed – lifetimes and explicit types, sprinkled with a mess of Pins on top.

You cannot run scoped fibers, forcing you to "Arc shit up", Pins are unusable without unsafe, and a tiniest change in an async-function could make the future !Send across the entire codebase.