I don't think people use Python because it's fast. It gained momentum because it has good libraries for data science and ML. Other languages, including JS, are far faster at this point.

However, the reason to use JS in particular is because when you have a lot of I/O blocking calls (DB calls, web requests) it really is a lot faster. But if you do anything with numbers, JS is the wrong language - it's so limited here that it's almost laughable. Same with dates. That makes it a very bad choice for data science.