A lot of these notes follow a similar pattern: we start with Python, get a working program, and then rewrite it in X with a huge performance gain.

That’s fair. We use the easy language to get a correct program, then we use the “hard” language to get a fast program, now that we know what a correct one looks like.

This is the key here. If you try to start with the lower level language, you might spend a much longer time getting to the correct program.

It’s much easier to optimise a program that’s working than to debug one that isn’t.