It's good to point out this risk, but as with all maxims, it can be wrong depending on the details. Many big companies have been built on platforms, after all. In fact, as far as I can tell, one of his examples of "boring" companies that doesn't fall victim to this is Square, and Square is built on top of a platform. It's built on top of the credit card network. But VISA didn't kill them. Why not?
You have to look at the likelihood that the incumbent will enter your market. This depends on the threat/opportunity you pose. It also depends on the technical assets and abilities of the incumbent. It also depends on the opportunity cost the incumbent will incur. It also depends on the strain it will put on other lines of business. If the incumbent has to rewrite much of their business processes to compete, they'll be less likely to do so. You have to look at how open the platform is, and how likely the incumbent is to change it in order to kill you.