As an Arch user I've always been a bit confused by the joke. I have more shit go wrong on my Macbook. Sure, on Arch I might get a bad Nvidia driver update and either have to roll back the driver, kernel, or both[0] but these are at least easily fixable. You can easily determine the problem, fix it, and you've learned how to avoid it or resolve it in 5 minutes if it happens again (thanks Nvidia ;). Other than that, the only breaking things are when I'm fucking around, and well... that seems like my own damn fault lol. But several Macbooks I've had will go to sleep and if I try too fast to wake it up I'll have a black screen that can't be recovered until I reboot. And I could go on about how weird and infuriating some shit is and how I can't even implement a fix myself and I just give up because I don't want to waste time fighting Apple and play that cat and mouse game with no good documentation. I've just come to understand that "just works" means "not as buggy as Winblows".
AFAIAA the joke comes from Arch's purported superiority (rolling release, close to upstream, bleeding edge, KISS) as compared to "bloated/slow" e.g. Ubuntu. It's kinda old now and existed even before the controversial switch to systemd from SysVinit/rc.conf.
On virtual routers there is no content in /rom. What you can easily do is install another copy of the same image on another VM or container and run it through firstboot. Make a backup and compare it with a backup from your running system. Even better is to make a backup just after firstboot, then use the system and compare your current backup with the first one.
Do keep in mind that the OpenWRT backup does not contain information about which extra packages were installed after firstboot. I solved this adding a cron job which runs opkg list-installed > /etc/opkg_installed.txt and adding that last filepath to /etc/sysupgrade.conf so it gets added to backups.