I tend to agree with the answer to your linked question. It's not that it's the only way that works; it's that it's the only way that guarantees a clean installation. If you attempt an
apt-get dist-upgrade you might end up with inconsistencies in your system, where some of the old Ubuntu packages are left over and conflicting with the newer Debian packages.
I ended up following these Debian Bootstrap instructions when I did an Ubuntu -> Debian migration a couple of weeks ago on a home server. The process allows you to install Debian from a running Linux system, which worked for me because a) I was installing Debian to a separate hard drive, b) I wanted to perform most of the installation steps via SSH, and c) I'm crazy enough to try it. I'm still tweaking the result, and wrestling Grub into shape post-install has been a mess (especially since I have to move the keyboard over from the workstation anytime a boot goes wrong).
Bootstrapping is something of an intricate process, and if you're not experienced with Linux it's not something I'd recommend. But it's a good learning process if you're up for it.