I have never ever thought avionics software development would be in such a condition that you described in the link.

I am surprised to say the least.

I have always imagined avionics developers in a different way. Like having a thick rulebook to go through to add a new line to codebase etc.

Keep in mind my experience was almost exclusively with communications systems, which are important but nowhere near as vital as things like autopilot. Things could very likely be better there, or at a different company. And even many of the things I worked on were like you describe. There is a lot of red tape and testing to make certain changes, and the industry documents are often strict. But it wasn't always clear how much of that actually made things better/safer and how much was just fluff.