If you're cannot parse the configuration file, you don't update. It is perfectly, 100% stable, about 60% of the time (when I change my config file without an error).
nixOS appeals to niche audiences who like to brag about it. I think it is not a good idea to base everything on config files, since there is a lot of room for user error
You've literally described Linux. Wasn't even a week ago we had a circle jerk on here about how great it is that everything on Linux is an ascii file (technically inaccurate on most distros) rather than a nasty nasty database where the most you can fuck up at a time is a single entry vs breaking the schema of an entire file.