It's not inconsequential in my mind because as a power user I don't a-priori care about the site enough to have a reason to open the dev tools. What I'm missing is the indication that there even is a problem of some sort, and that if I wanted to see the problem details, I could open the dev tools.

In other words, as a power user, I want to know if the site has a "You problem", and the only explanation I fully accept for why the modern web doesn't notify users about website errors is that it allows companies to save on QA costs.

Their point I think is that often (to varying degrees), 'power user' things are less convenient to do or behind configuration options or menus and so on nowadays.