Who claims Python is slow?
Python is definitely *fast enough* for most things out of the box, and makes many performance optimizations such as splitting processing of large lists to multiple processes, setting up an LRU cache for any function, etc. incredibly easy compared to most other systems.
Additionally if pure Python is for some reason too slow for you in some scenario, there’s always PyPy, Cython, extensions, etc. and often there are already pre-made solutions for the most performance critical areas (e.g. NumPy).
The amount of tasks where the speed of Python would become an issue is very limited and most of those are anyway going to require special tools, but with things like MicroPython, Kivy, Qt, Pyglet, etc. the list is getting really short.
Anyway, fully agree that on top of all this the most important thing often is productivity - you want to optimize your own time spent, rather than the CPU’s time spent as CPU time is cheaper than your own time in most cases.