Unfortunately you can't make things faster by making them concurrent, at least not in the way computers are currently designed. (And they're probably designed near-optimally unless we get memristors.) In my experience it's the opposite; you can make concurrent programs faster by removing it, because it adds overhead and they tend to wait on nothing or have unnecessary thread hops. And it makes them more power efficient too, which is often more important than being "faster".
Instead you want to respect the CPU under you and the way its caching and OoO instruction decoding work.
I believe one of the reasons Rust got so popular is that it made concurrency much easier and safer right at a time where the need for it increased significantly.
If that is the recommendation, maybe the standard library could focus on easily spawning and coordinating multiple processes instead, with very easy to use process communication.