> when you async call a function, it does eagerly evaluate until the first suspend point. This is less overhead than immediately suspending, plus it removes the dependency of the language feature on a userland event loop.

This seems wrong. There's no more overhead for Rust's approach- which to be clear immediately suspends only the callee, not the entire stack of async functions. In fact, if you immediately await the future, the control flow is literally no different from eagerly evaluating until the first suspend point.

There is also already no dependency on a userland event loop. This is, again, because only the callee is immediately suspended. It's still entirely up to specific leaf future implementations to interact with (or not) the event loop.