While I understand the motivation, and agree with it, I think that this part is a bit too abstract for the chapter. I would push for making things a bit simpler, while keeping the general message: ie worry about the algorithmic complexity.

Suggested action points:

* Start with a simple message, for instance in a "sidebar" directive, something like "Often choosing the right algorithm matters more than writing optimized code"

* Rename "complexity theory" -> "Using better algorithms: algorithmic complexity"

* Remove the "big oh" notation part. It's not necessary to use the notation and the name. The concept of algorithmic complexity is enough by itself.

* Use the "tip" directive to be able to fold away many of the discussions, so that when we give a course using this material, we don't scare away people.