@RedGlow one more reason to consider Debian - it is the official (new) Steam Runtime. What you get from building & testing natively should match closely with what happens inside the runtime.
@RedGlow SteamOS itself is still the Arch fork Manjaro, but any game running inside of Steam doesn't get to see much of that. Games are run inside a "pressure vessel", where they are told to use the libraries and whatever other environment details that come with the runtime. I'm pretty sure the runtime has always been based on some (usually ancient) version of Debian.