[nottathrowaway3]

> I have the conclusion opt-in async/await is a mistake. I think high level language/runtime like c# should handle it automatically...

This is not a good idea unless you like having to make all your code thread-safe (well, async-safe). Explicit declaration of "hey this method might not run all at once or be interleaved with other methods" is a good idea; explicit opt-in is the same in every other implementation of async/await (ex: js).

[serguzest]

I don't understand. Async methods can call sync methods already, how it is not mixed already?

Nope, it is not same in every other implementation. e.g Golang.