Performance should not be sold as a new feature; it should be one of the main drivers from the beginning. I remember reading the verge redesign article where they raged about the speedups compared to their previous site - and the new was still bloated.

I have no idea what that section is trying to say? It isn't a feature but a requirement is the common argument. It isn't a primary feature but a result of following minimalist criteria is another..

The example that a long book of text downloads in a second seems to be saying the latter..

You are right, sorry. When I first read it I internalized it as meaning to say that Performance is not an extra feature that you tack on to an existing web app (like you would implement say an offline mode as part of an update) but rather something that needs to be considered from the ground up right in the design stage. But I can see how putting it this way could be confusing.