If the thread can be dropped while the buffer is "owned" by the kernel io-uring facilities (to be given back when the operation completes) that's not "unique" ownership. The existing Rc/Arc<T> may be overkill for that case, but something very much like it will still be needed.
Slapping Rc<T> over something that could be clearly uniquely owned is a sign of very poorly designed lifetime rules / system.
And yes, for now async Rust is full of unnecessary Arc<T> and is very poorly made.
If the thread can be dropped while the buffer is "owned" by the kernel io-uring facilities (to be given back when the operation completes) that's not "unique" ownership. The existing Rc/Arc<T> may be overkill for that case, but something very much like it will still be needed.