Right, but is it true in the absolute that dependency pinning is flakes’ killer feature? Not clear to me, considering stuff like Niv exists and does this too.
The killer feature (for me at least) is that it does that while being (or having a chance of becoming) part of standard Nix, with all that this entails (see e.g. the discussion here).
Meaning you don’t need to mention Niv, just scale down (or qualify) the claim a bit.