Project Valhala has the goal to be ABI compatible with existing JARs, hence why it has taken so long, they want to add value types semantics without breaking Maven central.

C# can be much better, or it can be much the same. It depends on which implementation you use. Standardisation is an issue here, the system library has the "Nullable<T>" struct (1), but not a standard Result<T, E> class (or struct). Popular libraries such as "OneOf" use a class type. The single-valued "OneOf" type is effectively an "Option<T>" (2)

Nullable<T> itself is not exactly the same as Option<T> since it does not cover types that already allow nulls. It adds nulls rather then removing them.

Many people roll their own Option<T> or Result<T,E> type, since it's easy enough to start, and it's usually a class type.

1) https://learn.microsoft.com/en-us/dotnet/api/system.nullable...

2) https://github.com/mcintyre321/OneOf/blob/master/OneOf/OneOf...

C# does indeed produce a rather tight assembly

https://sharplab.io/#v2:EYLgtghglgdgNAFxBAzmAPgAgLACgACATAMx...

Well, Valhalla is described as “requiring 7 PhD’s knitted together”, doing that while remaining backwards compatible is insanely hard.