Bending the question a little but my second "first impression" of Arch's "simplicity" surprised me the most.

I was running Gentoo for a while before deciding to move back, and I was surprised that somehow I had

• saved space
• gotten faster at doing new things (...)
• didn't lose any boot speed or anything like that

Granted, I had jumped on Gentoo because of misconceptions (speed, ricing, the idea that I needed USE flags), but going back, I saw things more clearly:

• the AUR being basically a shell script download + 300 MB of base-devel was simpler and more space-efficient than /var/db/repos (IIRC -- since the portage and guru ebuilds were all held locally anyway after syncing, an on-demand AUR saved space).
  • the simple automatic build file audits on Arch felt more clean to me. I like checking my build files; had to make a script for the guru ebuild equivalent (but maybe there's a portage arg i missed somewhere -- wouldn't be the first time)
• Arch repos separating parts of packages in case you don't need some part (like splitting some font into its languages, or splitting a package into x and x-doc and x-perl) was almost a simple USE flag-ish thing already
• /etc/makepkg.conf was Gentoo's make.conf. And its build flags looked similar to the CFLAGS I manually set up anyway.
• My boot time (btrfs inside LUKS with encrypted /boot) was the same with systemd vs. openrc
• I realized I liked systemd (because of the completeness of my systemctl muscle memory, like with systemctl status and journalctl, or managing systemd-logind instead of using seatd and friends).

Not bashing on Gentoo or anything, but it's when I realized why Arch was "simple." Even me sorely missing /etc/portage/patches was quelled by paru -S <pkg> --fm vim --savechanges.

And Arch traveling at the speed of simplicity even quantifiably helped: Had to download aur/teams the other day with nine-minute warning.

¯\_(ツ)_/¯