Gentoo is flexible -- perhaps maybe a bit too much so for most people. And it requires a lot of setup. Arch starts small, but it's not minimalist. There's a specific philosophy to most distribution families. It so happens that Arch Linux' philosophy is similar to that of another OS that I love: OpenBSD.
Arch values code correctness and cleanliness over convenience. They start you out with a small but powerful core that doesn't have a GUI or many fancy apps installed, but they provide you with everything you need in order to have your ideal setup running pretty quickly. While most Linux distributions make broad-sweeping assumptions about what the end-user will want or need to do. Flexible operating systems do no such thing. They might require a little bit more work to get set up, but what you end up with will be precisely what you want, not just something that you can make work.
Also, HiR got about 3.5 seconds of fame via Mubix on Hak 5 Episode 621 (a little after the 3:00 mark). Mubix mentioned most of what he was doing with FreeBSD was shell stuff. All of the BSDs require some work to get all configured and ready to use with a GUI, they don't go too overboard on assumptions.
For example, the things I do first on both ArchLinux and OpenBSD:
- Set up package repositories. In OpenBSD, set PKG_PATH to the URL of a package mirror. In Arch, un-comment some lines in /etc/pacman.d/mirrorlist
- Install sudo and give the %wheel group sudo access.
- Create a user-level account, place it in the wheel group.
- Log off, log on with my user-level account
- Start adding packages and setting things up!
It's up to you to figure out what packages you want. X.org, a window manager, web browser, IM client, a word processor, and your favorite CLI tools are probably the first things you'll want to set up. Or maybe you just want an AMP web server. Flexible OSes do both of these things well and without much fanfare. Truly, you make your own distribution with every install.
Arch Linux is interesting in that there is no "release" schedule. You just perform "pacman -Syu" to upgrade all the packages to the latest stable version. Upgrading OpenBSD can be a bit more of a pain, so I genuinely like how Arch handles it.
Minimalist distributions (DSL, TinyCore and Puppy Linux come to mind) still make too many assumptions. Although they're tuned for systems that have limited resources and they can be tweaked and expanded quite a bit, you may find that the partitions aren't configured the way you want, that the organizer included applications that you don't need, or worse: they compete with the applications you'd rather be using.