HN, which is about as fast as sites get in my experience takes between 600ms and 800ms to fully load with cache disabled. Around 350ms to load just HTML and CSS.
IMO a few hundred milliseconds for something that is actually webapp-like rather than just an information website is quite reasonable.
Notably, the examples in the OP article are slower by many thousands of ms, not just hundreds.
Either way, the post isn't saying you have to abandon app-like experiences. It's only about improving initial HTML delivery regardless of what you do after that.
IMO a few hundred milliseconds for something that is actually webapp-like rather than just an information website is quite reasonable.