Not true from what I've seen Every C# library with support for async/await has synchronous versions of those same methods. In fact, Microsoft's own documentation recommends appending "Async" to the method name for precisely that reason - to distinguish an async method from a sync method.

Furthermore, "asynchronous" code doesn't need separate threads. A scheduler and green threads is more than enough.

Have you seen Go? You should take a look at it. It makes writing concurrent code basically trivial, using "green" threads and channels and a neat little "select" statement.