Yes, pacman -S package will install the version of the package that is listed in the current package database, and will not do anything to update that database.

I mean if the current system is truly ancient and doesn’t support UEFI I could imagine it ceasing to work, or something like that. But that should be easy enough to fix.

As a long-time Linux user I can’t say I’ve noticed big changes in the last 10 years… Maybe I’m forgetting, but when I first used Linux on a desktop I had to compile drivers from source to have working graphics acceleration and WiFi. Things have come a long way since then, but by 2015 I feel like those big things were all sorted. There are still many small things but I think most of those are unchanged, too.

widespread adoption means you can get things like contributors who will then work on optimising battery life and other fundamentals.