Im not quite sure what you are getting at JaM. What we are saying is that the armour upgrade system works. So that despite the unit card only showing an increase in defense of 2, a unit going from flesh to light mail will infact have an increased armour factor of 5.

So armour upgrades are working properly, just the incorrect details are shown on the unit card.
The whole method you are suggesting is quite hard to implement from code perspective> Just imagine - game has specific file for units, there are values for protection of unit,but it is not used, instead of this there is some other table where upgrade 1 means armor 4, upgrade 2 armor 5 etc... That dont make sense.
It actually makes quite a bit of sense, as it allows them to define an armour system seperate of the unit stats, with the armour values in the edu allowing for more initial variety.