gonna throw my two cents in here for python if all you're doing in local modeling/forecasting. Super easy and it's plenty fast (I use it on a 5000 stock universe every weekend...) Google "python rsi". You'll find a Stack Overflow solution that does exactly what you're looking for.
nodeJS is written in C/C++ so that's impossible. Most of the benchmarks are faulty to begin with. When done properly, C/C++ is magnitudes faster. Python is slower but no-one really uses native python for any larger datasets, modules are used which implement C/C++ underneath.
There is just no reason to not use NumPy. There is no point in comparing "python vs C++". Your implementation in C++ is not going to be faster than NumPy. That doesn't even touch on the ecosystem you are then getting for free.
Would it be a faster way to learn whether your idea works to sign up on TradingView and write/backtest a strategy using their Python-like language?
Is it possible to develop in Python and execute in C++? The platform I use is developed in C++ and I'm not sure I can build in Python and execute in C++.