"What they mean by IO bound is actually that their system doesn’t use enough work to saturate a single core when written in Rust: if that’s the case, of course write a single threaded system."
Many of the applications I write are like this, a daemon sitting in the background reacting to events. Making them single threaded means I can get rid of all the Arc and Mutex overhead (which is mostly syntactic at that point, but makes debugging and maintenance easier). Being able to do this is one of the things I love about Rust: only pay for what you need.
The article that this one is responding to calls out tokio and other async libraries for making it harder to get back to a simple single threaded architecture. Sure there is some hyperbole but I generally agree with the criticism.
Making everything more complex by default because its better for high throughput applications seems to be opposite of Rust's ideals.
I don't think its a matter of being "smart enough". Human error can easily creep in when dismissing 10's or 100's of prompts.