They have resolved this exact problem. There is an “experimental” cli tool that fixes a lot of your complaints about nix-env, nix-channel, etc. Itcs wrapped together with “flakes”. This newer feature is a little different, and working with or without flakes segments the community AND the types of articles about nix, like this one.

As far as I know though, nixos related thing still have a bizarre set of commands, and even with flakes “nixos-rebuild switch --upgrade” is still how you switch configs.

And as far as installation goes, using nix-env -iA really is a bad practice. Thats installing something ad hoc like you would in any other package manager. That defeats the point of nixos, where your configuration file explicitly defines all the packages you need installed, and nothing else. Nix will remove any packages you didnt specify.