As a 15 year full time JavaScript developer I think Blow is 100% correct.
Seriously consider what would happen to these jobs if tomorrow things like Vue, React, Angular, Express, Spring (Java), and so on all went away. Most of these people become instantly irrelevant even though demand for products/development in this space will remain constant. Those people are tool users, like screwdriver users who call themselves carpenters. WTF, why and how did we get here?
Programming is programming regardless of whether you are making AAA games, building a web application, or guiding rockets to kill people. Programming is a skill. Employment, however, is not so straight forward. Employment is a game in the same way "musical chairs" is a game and people will chase money irrespective of skills. Games are meant to be won.
The problem is a supply/demand problem. Historically the demand for "web work" (however you want to define that) has been high but the necessary preparation has been astonishingly bad. Most developers are trained by universities to write in something like C++, Java, or Python. Employers solve for this not with training (because that costs money and developers cost money) but with abstractions. The result is a platform that scares the shit out of the people hired to write for it. This is the inefficient that Blow is describing and its very real.
As an example consider the DOM. The DOM is the compile target of the browser. If you are working on the front end that is your foundation and everything layers off of it. Yet, the DOM is a tree model and tree models irrationally scare the shit out of people. The level of hysteria this generates defies the imagination. Most developers would rather be in zombie apocalypse combat than writing to the DOM directly. It's weird.
Another example are JavaScript classes. Why would you ever need classes if JavaScript has native lexical scope, functions as first class citizens, and a scalable object system? Maintainers of the language thought the same thing and were extremely resistant to add classes to the language, but classes were demanded in the ES6 specification almost more than all other features combined. The demand exists because people were/are educated to write code in one way and could not imagine writing code without that one way of doing it.