Calculating mandelbrot fractals to measure speed might be a nice exercise in which Rust or Zig can compete with C. But in a real software implementation, when you need to open a file you still have to call the OS function fopen(). Whatever thing File::open (Rust) is doing before calling fopen() is overhead.

How can you avoid that overhead? Write in C (at your own risk).

This is why we keep seeing the “X is faster than C” articles: if you use the standard C library in a sort of not great way (sscanf) vs a more intelligent version of the code in another language you will get faster than C results. But on the whole doing less work is always faster. Not doing bounds checking on an array will always be faster than doing bounds checking. How could it not be? No amount of computer science can make bounds checking take negative time.

I am not saying C is magically faster. I am saying that by letting you not do critical safety checks it will be faster. Rust has a similar capability for some things but if your goal is to write unsafe Rust for the sake of performance, then is it worth the switch?