Python is a remarkably versatile and powerful language. It is heavily used in applications which require heavy CPU number-crunching capabilities, leveraging toolkits like NumPy, SciPy, PANDAS, MatPlotLib, Seaborn, Jupyter and many others. There is nothing “slow” about Python in these applications!
Also it is very popular as an extension language in many open-source apps, not just Blender. It is instructive to compare Maya and Blender in their adoption of Python: one just introduced a straight transliteration of its existing rubbish scripting language (MEL), while the other integrated it completely into the entire app, making every object in a Blender document directly accessible as a Python object, behaving according to common Python idioms.