Whereas Rust makes you write complex code because they put a lot of work into making a sophisticated compiler. It's a strange case of convergent evolution.

curve25519-dalek is 3X faster than the equivalent Go code (i.e. in the stdlib, authored by agl).

This is for a few reasons:

Rust has support for 128-bit integers (i.e. u128) which allows for faster arithmetic when operating on what are effectively multi-u128 bignums in an elliptic curve library.

LLVM is generally more sophisticated about optimizations. It wasn't until recently that go had an SSA-based compiler, so its optimizer isn't nearly as sophisticated as LLVM's, which has been developed for many years now.

My information may be out of date, but last time I poked through the Go compiler, it did no vectorization or anything equivalent to march=native. So there's plenty of opportunity for Rust to be faster.