I understand where you're coming from, I love NixOS and it seems like it could be well suited in a way, but it is extremely complex to learn Nix, and it doesn't have the scale or support Arch does, on top of being a massive departure from the typical distro and I think Valve want the Steam Deck to be a straight up portable PC.

Being pragmatic about it, I just don't think NixOS was ever a contender.