Does that matter? If there is a stable driver that's what's important, and FreeBSD has if anything a better track record for maintaining drivers for longer, even if those drivers were originally ported from elsewhere.
> Linux is undeniably a safer, more conservative business decision than FreeBSD.
I disagree; safe and conservative is exactly what FreeBSD does better than Linux.
For example, a lot of the tricks that Proton relies on explicitly use patches to the Linux kernel to do with FUTEX_WAIT implementation, which have only been patched into mainline since 5.16 afaik, as well as bleeding edge Mesa/xorg versions, the current state of things is that it makes sense for them to base on a rolling release where they can frequently push system images with bleeding edge versions to the deck hardware.
Maybe a few years down the line it'd make more sense to base on something more stable like BSD, but things are moving very quickly in Linux+wine gaming support and it's actually helpful right now to be on experimental/unstable versions of certain things.
Bullseye is the good enough point for basically everything other than gaming on debian distros, not much you can't do with juat the bullseye repos.
Now that Valve has decided Linux gaming is a real thing, within a few years Debian will probably be good enough for that..
Not that it will stop them from constantly changing stuff in breaking ways for 3% better performance....
The only thing Sony needed from FreeBSD was x86 support and generic kernel facilities such as memory, process and IO management. Everything else they wrote themselves for their proprietary hardware and userspace.