For me, the ease of use of PKGBUILD files makes it easier to interface external or modifird software with the system (this has led to success of the AUR).
Apt itself is great, but the PPA repos that make every dist upgrade more complex is kind of not nice. With pacman you have AUR and very simple package scripts, that lets you easily add whatever to your system that's not included in the distribution.
With apt this is not that straightforward.
There is "checkinstall" that creates an apt package by watching changes during a "make install" step. So you can install many programs that don't provide .deb packages or only provide source code that way.
Imo, both are kind of sucky. (Just install a gnome group on each, then remove it and install plasma and see how many non-used service whatever continues to be installed). Nix is the correct solution to the dependency hell problem.
Nix could allow for home installs, however. It would make it useful in a lot more situations.
What do you mean with home installs? Installing nix itself without root?