> This may come down to how good the language is at capturing desired semantics in a library. Rust still has a long way to go to catch up with C++ on this axis, and C++ is not waiting around.

What catch up does Rust need to do?

Rust has slice that know the size of its data built in the language, while C++ doesn't. And Rust has stricter const and mutability rules that facilitates optimizations.

As for the implementation, Rust use LLVM which is also the backend used by one of the popular C++ compiler.