I think you have confused the apt command with the apt-get command. apt-get doesn’t handle files, while apt has it since the very first version. This is one of the important differences between the two commands. This was one of the main reasons why I have been using only apt for years.
I’ve already tried MX Linux on an old Thinkpad SL400, and didn’t see any difference from plain Debian.
Because it’s the stock Debian + custom themes/skins + some crappy useless minitools. The 99% of packages come from the official Debian repository, the rest are only the rice.