1. Amdahl's law

2. That's a language feature too. Writing non-trivial multi-core programs in C or C++ takes a lot of effort and diligence. It's risky, and subtle mistakes can make programs chronically unstable, so we've had decades of programmers finding excuses for why a single thread is just fine, and people can find other uses for the remaining cores. OTOH Rust has enough safety guarantees and high-level abstractions that people can slap .par_iter() on their weekend project, and it will work.

Given most machines have cores to spare, and people want answers faster, is that a bad thing?

I think the complaint is that the C version isn’t multi threading ignoring that Rust makes it much easier to have a correct multithreaded implementation. OP is conveniently also ignoring that the Rust ports that I reference Russinovich talking about are MS internal code bases where it’s a 1:1 port, not a rearchitecture or an attempt to improve performance. The defaults being better, no aliasing that the compiler takes advantage, and automatic struct layout optimization all largely explain that it ends up being 5-20% faster having done nothing other than rewrite it.

But critics seem to often never engage with the actual data and just blindly get knee jerk defensive.