> Writing HTML back then is very similar to writing it now
Not at all. The author may have gotten some minor details off, but all of that was present on some level in various quantities. I worked on enterprise software back then and it was a matter of editing HTML in ASPX to manually update your JS libraries. It was also a matter of manually linking your HTML tags to thousands of lines of CSS in typically a single file. It was a gigantic pain in the ass to do on a large code base with hundreds of pages and it meant acting like a human compiler/package manager, carefully grepping through to make sure you didn't miss something when you upgraded JQuery to version 2 or that your CSS class rule didn't accidentally cascade changes to some non-related context and throw your div 16px off-center. It was mind-numbingly dull and extremely error-prone.
It was back then that I realized that despite the fact that some of our web code was written in server-side C#, it by no means could keep up with the need to make dynamic fluid interfaces on the client-side. The lines of code in JS had grown higher than the lines of C# over many years. And yet the tooling was still treating JS as if it were an animated cursor plug-in. It did not have first-class tooling just yet, and JS was missing some critical features (like native modules) that would make it better to work with. This is at least part of why JS was hated so much back then and there's still quite a bit of hate that lingers from that era. It was very frustrating to work with.
It got dramatically better over the next few years, but there was a lot of churn between Bower, yarn, npm, webpack, etc. Even Node.js I believe split off into io.js back then until it re-merged. AngularJS was originally adopted because it solved a lot of these problems for devs with a kitchen sink solution, but it did so in a proprietary, non-scalable way. The JS ecosystem eventually surpassed Angular's capabilities and now we're able to freely move between React, Angular, Vue, Solid, etc while still using the same tooling.
Centering divs was still surprisingly difficult in 2012. Flash was already on life support, for sure, by then, but Flash websites were still out in the wild. Everyone was waiting on HTML5, but it took a couple of years for IE to get retired, for Edge to get released and for Safari to catch up to much of the spec. IE was still a significant market share then. CoffeeScript was at its peak in popularity probably in 2012. The author got a lot very correct in this article. The gist of what they're saying, though, absolutely true.