There's the primary maintained software repository, then there's the AUR. I think most of the times people's systems break because as inexperienced users they find a specific piece of software a site told them to install and its only available in the AUR, instead of finding something properly maintained that already exists to do the same thing. Over time you end up with a mess of a system relying on user maintained build files.

I learned a lot in my first year of Arch (probably my 15th+ year of Linux though and I was not afraid of the command line) so I decided to reinstall my system after that first year and one of the choices I made was to not use AUR packages (except in very specific cases). I also changed bootloader's and a few other things.

I've had mine break twice I think. The first time was because I didn't know the general rule was "if you're doing an update, update everything". I saw an updated GPU driver was released so I installed it, but didn't bother with anything else. Turns out you're supposed to update the graphics drivers and kernel at the same time, so i wasn't getting output after booting the kernel. The beauty of Arch though is that when you learn to install it, you also learn how to fix it. Booted off the USB installer stick, mounted my root partition, chrooted to it, then ran a system update. I was back booted up, logged in, and gaming in less than 10 minutes from discovering the problem.

In general, I would say people's systems getting bricked "all the time" is a bit hyperbolic.