Java is very methodical about what features they add. Some of the sluggishness is intentional.

As far as threading, Java is adding userspace M:N threads which will be far superior in most use cases to C#'s async. And unlike async it gives an automatic performance boost to most existing code

C# has a long history of breaking changes. One of the reasons Java is more popular is 90% of decades old code runs fine on the newest version. Java's backwards compatibility is absolutely unmatched.

Project Loom’s virtual threads will be superior to the random function coloring with async in C#. With it, you can write sync code and it will automatically change to another “fiber” when it hits IO or other blocking operation.