Isn't every distro a custom distro, by definition?
Anyways, I get that this is a "risk" to consider, but installing a new distro isn't so bad that it should prevent one from trying and using a currently extant distro if it works for them.
I'm not sure I'd define the atomic Fedora variants as "distros" in the traditional sense.
This is a bit of an oversimplification, but Bazzite, Bluefin, etc, are basically just Dockerfiles that use Atomic Fedora as the base image.
So you are basically getting a pre-built docker container that is "Fedora + various configs added on top", and then you are booting that docker image.
Since it's just a container file, anyone could theoretically just fork the Bazzite repo, make some changes to the Dockerfile, then push it to github + let github actions build a custom docker image.
So is that custom docker image a distro? Some would say yes, others would say no.
Ironically, I'm considering installing Bazzite alongside NixOS because it's proven to be nearly impossible to run SteamVR properly with how Steam is packaged
From what I’ve seen so far from people I know who run Valve Indexes, Linux SteamVR performance is pretty poor compared with Monado+OpenComposite. Hopefully this situation changes with the release of the Frame, in which case I (and likely others) will be revamping the SteamVR package and NixOS modules as Monado may not fully support it for some time.
Tl;dr: Run Monado w/ OpenComposite for the Index, it runs way better.
Dropping back here to say that I have been playing around with Monado + OpenComposite + WlxOverlay and while it's been plenty janky, it has actually usable performance when it works.
They mean "custom" as "pre-configured to do <X>" where X is gaming. Generally most distributions are not pre-configured outside of a general suite of standard applications.
Anyways, I get that this is a "risk" to consider, but installing a new distro isn't so bad that it should prevent one from trying and using a currently extant distro if it works for them.