JS isn't particularly slow any more, thanks to the massive efforts invested in the optimization of the various competing JS engines. It is generally faster than Python 3 (http://benchmarksgame.alioth.debian.org/u64/benchmark.php?te...) and not just a little. Just for the hell of it I compared node and python on naive fibonacci. That is anecdotal, of course, but node is 30 times faster. I do agree with you that JS has horrid, bug-prone semantics, but it's impressively well optimized.
I also agree that other languages offer better tools. For instance, Python has Numpy. However, that's written in C++, not in Python. You can write plugins for Node in C++ too, so nothing would stop someone from writing a Numpy equivalent for JS. You might even be able to run it in some browsers through something like Emscripten with a performance overhead of 2-3x (I think?)
I also agree that other languages offer better tools. For instance, Python has Numpy. However, that's written in C++, not in Python. You can write plugins for Node in C++ too, so nothing would stop someone from writing a Numpy equivalent for JS. You might even be able to run it in some browsers through something like Emscripten with a performance overhead of 2-3x (I think?)