ITwebs What do you mean by "atomic"? I suspect there is some randomness in the setting of colour saturation and font sharpness each time when the phone is resetted.
Deterministic is probably the better term here. (e.g given the same unit of a device, DFU restoring it to the same iOS version and configuring it with an identical setup procedure should result in the same outcome every time). Now if Apple is randomizing certain UI settings (or whatever) for the UsEr ExpEriEnCe, that may be potentially be another variable to account for in data collection.
DFU restore, save for certain per unit calibration/serialization data reformats the internal NAND, whereas my (past) understanding of "Erase all Content and Settings" is that it attempts to erase userdata and settings from the running OS, so there's more liable to potentially "go wrong" there.