My point about removing stuff on Windows is you can't queue anything, so you
need to keep choosing the next thing to remove. You can't spend your time
playing Solitaire in only 10-20 seconds, and if you're removing more than a
couple things, it's an incredible hassle.
With regards to the shortcomings of gnome-app-install, that's only that
program; Synaptic (which is the native Debian package manager) works
perfectly.
With regards to Python, it's not lying when it says removing Python 2 will
break your system; a lot of programs (many of them important) are in Python.
But you don't need to remove Python 2 to get Python 3; I don't know where you
get the idea that you do. I have both on the machine I'm using (and
installing Python 3 is usually one of the first things I do, since I like
using Python).