I understand some of the points the author is making, and will have to give it a closer read when I'm not at work. But I reject the thesis at a glance. Most clients don't have time to deal with everything related to their web presence, custom or not. If you're solving business problems, not training them to use WordPress, you can charge a premium.
Posts like this strike me as comment and controversy bait (more specific than linkbait). An underinformed post whose points are stated too emphatically about a large topic.
Where I live I can clean my car for $ 8 if I drive to a place and do it all by myself. It will take me an hour to drive there, clean it and get back.
I can get it cleaned at the carwash for around $ 21, that will take me 40 minutes.
Or I can make an appointment and give my car to a guy who cleans it for me, the cost is $ 35 and it takes me 10 minutes.
They all make good money. Even the guy who charges $ 35.
But none of it is 'premium'.
There's a guy in Derbyshire, England. He charges £ 7200.
Now that's premium. But the market's too small for premium. At least where I live.