"What even is a good specification, or the Huaqiangbei test"
Those three points are pure gold!
I'd also add that you don't need to be working on a major project to benefit from standing back to writing it out first. Much of what I write is just a few pages, but it's still useful. It saves time overall, helps others get up-to-speed fast, and is fun!
Personal plug: I wrote an article about writing specs a while back. I use the IBM PC spec as an example, so you might find my article useful.
https://iskender.ee/2020/06/18/EE-Specs.html