To be honest I found it an incredibly comprehensive overview of Debian packaging, all the way up to using pbuilder to ensure dependencies and sandboxed builds, onto lintian to assess the quality of the artifacts.
https://www.debian.org/doc/manuals/maint-guide/
Building complex Debian packages is time consuming with a lot to learn, but to be honest I don't remember having many issues with this guide when I started out.
I didn't even know this guide existed, for example -- because of all the existing noise that exists in the same space.
I have managed to build Debian packages (and even self-host a repository) IN SPITE of the existing documentation, not because of it.
The guide I linked to used to be linked to from the main docs page I believe - I went to double check and it now has this more recent guide linked instead - it seems equally thorough.
https://www.debian.org/doc/manuals/debmake-doc/
These guides were sufficient for me to learn packaging pretty complex Debian projects, and are linked to from the docs home page on the Debian site. Guess that's all I'm saying.