Unless I'm misunderstanding something, this is precisely why I don't use Home Manager. I've literally never had my NixOS setup break over the course of many years.
In the very worst case, you update components individually until you find the offending one.
I've used both NixOS and nix-darwin for 2 years professionally now as daily drivers, and have had generally nothing but great success. I'm not fearing an OS update actively breaking my environment (which I can't say the same for macOS, as much as I am a fanboy of Apple).