This is great advice, and I'd generalize it the other way too. Ideally you want both founders to be willing to do whatever the highest value work is regardless

This is great advice, and I'd generalize it the other way too. Ideally you want both founders to be willing to do whatever the highest value work is regardless of how closely it matches their skills. We often put technical skills on a pedestal because there's a high bar just to get started, but often times building the next feature is not the most important thing you can do. Most people rationalize doing what they feel competent at, versus sober thinking about what is really needed and figuring out a way to do it well enough to get to the next stage. Eventually you can and should hire people do these things, but in the earliest stage having one or two brains fully dedicated to figuring out the repeatable business loop end-to-end gives you dramatically more agility and opportunity for insight than limiting yourself to well-defined roles and expertise.