Perhaps benchmarks should be compared on equal footing, say, with the default release flag or all optimizations turned on, otherwise they're improper.
But really the original author/poster should do some set on his box. I cannot even compile/run all his things. The point of my comment was just to give a reference for how far off impressions can be from build flags. PGO (available to Nim, c++, but maybe not to Rust yet?) is a whole other set of maybe nothing burgers or maybe big improvements.
(But, btw, I could not agree more that all experiments in this entire general space should have various big, bold disclaimers. Over-concluding from these things is rampant.)
For something super jumpy like a simulator, I would find it unsurprising for PGO to make up (or surpass) the difference to Zig in both Nim and C++. 20 years ago there was this ACOVEA [1] project to try to discover great sets of gcc flags that could often find 2X improvements in object code speed for me.
The range from build flags/procedures is often much greater than the supposedly interesting cross-language variation. These things often more measure developer experience/persistence than something intrinsic (and build flags/procedures are only part of that experience/persistence).
There are various debug things you can turn on, such as the race detector, the memory sanitizer, or coverage tracking.