While I use Python for ML myself, I find it weird to say that a language isn't slow because you don't really use it anyway. It's true that Scripts in Python can be fast if 99% of the executed logic is in C anyway but that doesn't mean the language isn't slow. As soon as your Python script needs to do anything not available in a library you'll notice how slow it really is.

Python is really neat to quickly experiment platform independent but it's definitely extremely slow.