There's a huge difference between everything you mentioned, and dealing with 'browser quirks' like:

  <!DOCTYPE html>
  <!--[if IE 8]> <html lang="en" class="ie8 no-js"> <![endif]-->
  <!--[if IE 9]> <html lang="en" class="ie9 no-js"> <![endif]-->
  <!--[if !IE]><!-->
  <html lang="en" class="no-js">
  <!--<![endif]-->

The points the author made simply aren't good arguments. Yes, frontend development was harder during those days, but not harder in a good or rewarding way.

That’s not what accidental complexity means. Accidental complexity comes from design errors that could have in hindsight been avoided, meaning that if those errors hadn’t been made (made by accident, literally), there wouldn’t be any accidental complexity. The items you list aren’t accidents that could be avoided, they are necessities in achieving relevant goals.

Sharding, buffering, caching, load balancing are mostly issues 99% of devs will never have to work on. It gets relevant on high load pages, but most stuff out there wont ever need it.