I do not understand what option do you mean.
The distinction between configuration and data is blurry. In this case, it is in datadir, not sysconfdir. Similarly, whether something should be hermetic needs to be based on case-by-case basis. In this case, since the config format is frozen in time, I agree that it is probably not necessary. I was speaking generally. Though, ancient software like xorg (not sure if xorg specifically) often do not have defaults and require some configuration file in /etc so hermeticity would be required if it were not so prevalent.