It's eye opening, because it shows how small the actual differences in executed code really are.

When I first tried this about 10 years ago, I was very surprised how good code Javascript JITs generated. I expected there to be type checks, lots of unnecessary memory accesses, etc. all over, but to my surprise the inner loop was practically same as gcc -O2 output when compiling an equivalent C program.

Of course the same is not true when it comes to bigger blocks of code, because Javascript does need to do a lot of bookkeeping behind the scenes.

I guess it is more like that many are still unaware of it when mixing languages with implementations, while arguing language X vs Y.