@redrum:
Hit differential is just 1 way of trying to have some sort of measure of “luck”. Its far from perfect but better than nothing IMO which was why I decided to add it. Each dice roll and battle have different strategic importance which is close to impossible to capture in any automated way.
I have considered adding a sort of TUV differential as well (actual TUV outcome of all battles - expected TUV outcome of all battles) but one problem with this is that its no longer a purely mathematical statistic as it takes into account casualty selection. Example being if you attack a stack of units that has say bombers then the battle calculator is optimized to try for best win percentage not best TUV swing where as a player may choose to save bombers longer than the battle calc chooses. This can cause somewhat subjective choices in casualty selection and the battle calc may not select the best which skews the TUV differential. This is even more drastic for maps that are more complex than Global such as Total World War as casualty selection is much less automatic and requires more thought.
Casualty selection difference is such a small difference on the scale of a match. Only a handful of battles require different casualty selection, and of those only a few changes the TUV swing significantly.