These perspectives were put forward when SaaS was really taking off and software hadn't quite eaten the world yet. The world has change a lot since then. Creating a new software product has never been easier than it is today. That should mean that competition is at its fiercest but we're also seeing a massive consolidation of markets and big winners with no apparent rivals.
I think Thiel's focus on defensibility is becoming more and more important for early-stage startups. Why bother proving out market demand if one of the big players snaps up the opportunity from under your feet. Executing well and moving quickly used to be good ways to defend against this happening but I think the established incumbents are not the slow lumbering giants they once were. They are now the software companies that won the market ten years ago. Maybe our strategies need to change to take this into account.