I think that comparing the best implementation of Rust vs the best implementation of C is an interesting thing to compare.

But if that's what this post is comparing, most of the content is probably incorrect, because the main reason C binaries perform better is because the C backend of the C implementation used is better than the Rust backend _for this particular application_. This isn't really news. There are hundreds of benchmarks comparing C and C++ using the GCC and LLVM backends, and each is slightly better than the other, depending on the application. You don't even need to write code in two languages to show this.

The authors appear to be aiming to compare how language differences affect the quality of the generated code. For that, you want to compare two equivalent-quality language frontends using an equivalent-quality optimization pipeline and code-generation backend.

This is, in general, not feasible. But for all languages sharing the same LLVM or GCC backend, doing this comparison is trivial, and would limit the differences to either the frontend implementation, or the language itself.

That depends on the purpose of the comparison. But for many practical reasons you are right.

It makes this statement seem a bit dishonest though:

"Our Rust driver is a few percent slower than our C driver, why? Well, it's of course because of safety features in Rust, but can we quantify that?"