Python is a toy for lazy programmer that never cared about performance. https://www.quora.com/Why-do-some-argue-that-Python-is-a-popular-but-bad-programming-language
With all that being said, “bad programming language” is a click-baitey way to summarize the situation. Of course Python isn’t a compiled language. Of course Python isn’t made for performance. Of course python isn’t made for web / mobile dev. Of course Python isn’t made for low level / embedded. But for everything else … It’s a solid candidate As for UI … I’ve never tried but in JS/TS. So I can’t relate to other languages.
Do you know what is Python good for? Pentesting. It has so many vulnerabilities that if someone can get to your machine and run Python, you are fucked.
the UI is not a major factor for me, but rather transitioning all such indicators and chart patterns onto a to-be-coded backtesting platform in the future. I like Java even its UI is not the best. Even I do like Nodejs, I am not sure if a browser UI is what I want, when it is possible to use JavaFX, Flask, RShiny for displaying a chart and backtest statistics. Why do you emphasize on the UI so much?
Incorporate godot or unity3d game engine. Can even use c# in them. VR goggles and zapping body parts when indicators trigger.
I'll leave you to it. Have fun. A library about trading indicators that does not display anything. A real success.