You can’t run steam with no compositor whatsoever, but you can use the steam deck’s solution of using their gamescope micro compositor for everything. You should be able to install gamescope and just run gamescope -e {other CLI options} steam (assuming you’re using the native Arch package and not the flatpak).
My experience using gamescope for steam has been very mixed, but I’ve seen a tutorial somewhere on doing exactly this.
Gamescope isn’t necessarily the best option for every game, and having a normal compositor (which, for now, must support XWayland) is just a much more flexible solution.
This may also be possible with something more general like xwayland-satellite, but frankly steam and all its games still run on the X11 protocol, so if you really don’t need a GUI you might be able to install a vanilla X11 instance and hook to that directly. I can’t speak to either of those options directly.
But is this worth it, in a practical sense? No. You have a reasonably powerful system, and the only performance you’d be saving is a few percent of a single core on the CPU, which in your config is absolutely not worth it.
Ahhh got it. I thought it was a “I know this is inadvisable, but dammit I’m going to do it anyways” type of post :)