If all you want to do is play steam games then I'm sure steamOS is going to be the best experience possible. If you want to use it as a regular PC it probably works reasonably well but a user who doesn't want to use the terminal is more likely to run into a brick wall at some point (e.g. connecting to a printer or something). Something like Linux Mint is going to give an overall friendlier experience for someone new to Linux even if running steam games on it is slightly less friendly.
Ironically connecting a new Brother printer was the most painless thing I've ever done on Linux, because I didn't do anything at all. Linux saw it appear on the network and it just worked.
It certainly can be for newer printers. I guess my point was that, at some point, you will run into a problem. It might not be connecting a printer but, with an Arch based distro, there is a high likelihood you will need to do some cmdline stuff at some point. In a Mint etc that likelihood is smaller.
New printers implement the print server themselves, which I assume is why CUPS driver support is being deprecated. Basically, they're all HTTP* servers so no driver/etc support is needed.
