While SteamOS is Arch based, i don't think they really use it the Arch way.
It's run as an image based immutable OS, so they control the packages and not run at the bleeding edge.
You might run into problems more likely than SteamOS will.
Although i didnt't have problems gaming on Arch, it's not the same
I think they confirmed in an interview at one point that they don't roll with it. They take the binaries they need from it, test it and freeze it. Initially they were using Debian but ended up needing more recent package versions and apparently Arch binaries in core and extra were more suitable to their purposes than Debian testing.
Valve was using Debian way-back-when, but the pace of getting new stuff into debian proper is too glacial for Valve. Valve is putting a lot of work into "making the linux graphics stack rather good for games", and having those improvements integrated upstream quicker means that Valve can get to work on the next set of improvements.
Valve is still using Debian as the basis for their runtime environments for games (pressure vessel). Debian's slowness is great for providing a stable ABI for the parts that come into contact with (seldom maintained) game code. There is some amount of magic that goes into gluing the stable runtimes with rapidly changing stuff like Mesa.
Arch installs aren't too bad, it's the post-install setup that'll get you though since a fresh install is guaranteed to detonate if you don't disarm it.
It doesn't even have to be complex anymore thanks to archinstall.
Sure, but newbies aren't super adept at reading the arch wiki, which is excellent but still intimidating for the inexperienced. Also it's pretty easy to break something that you don't know how to fix, and the folks on the arch user forums are as likely to RTFM you as they are to actually help.
Most people who just want to play some games understandably wouldn't want to get out in the weeds of creating disk partitions from the command line, no matter how well the wiki holds your hand.
it definitely taught me about how linux works, at least the parts that are relevant for most users. starting from a clean install without any kind of gui (or common networking tools) really made me understand all the building blocks modern desktop linux uses. sure, installing a full blown desktop environment skips most things, but going with just a window manager and adding required features package by package really does help with understanding, and if a problem does pop up later you'll know exactly where to look, instead of having to search super generic terms.
Just because Linux as an operating system can have that experience, doesn't mean everyone wants or, really, needs that experience. Some people buy cars to drive and want it to just work. Others buy cars to play with. Some people dj music that is already made, others buy a guitar.