The key takeaway from the article is that Medium is still under 50 people. At that size, any sort of hokum management style will probably work. Call me when you hit 200+.
Gabe Newell is on line 3. Valve is famous for their flat organizational structure. At nearly 200 people and multi-billions in revenue, it can work. Ofc Valve does a lot more than a simple blog site.
Any sufficient large group of people will self-organize into hierarchies. A refusal to write it down doesn't prevent this from happening, it just means people are even less accountable for the position they occupy.
"We believe in flatness" usually is code for "we believe in the appearance of flatness".