From @jgraham (via gh-16339):

As a high level point, I don't think that wpt serve and wpt run are easily interchangable workflows. For example if you only care about running in Firefox and Chrome there's no need to edit the hosts file for using wpt run, so there's a considerable simplifciation in that case. The fact that wpt run can install fonts for you is another example of where it's simpler.

I suggest the documentation initially covers wpt run and then provides detail on the extra steps in order to do everything manually using wpt serve.