Then you look into it a bit more and the story changes to "oh actually you need to enable this experimental feature to get better reproducibility".

This unfortunately gets misunderstood a lot, mostly because of the stupid flake hype. You do not need flakes for reproducibility, Nix comes with a fetchTarball builtin function which allows you to pin a specific Nixpkgs commit and output hash.

You're right though, I agree on basically every point (including the part about flakes).