I don't think that requiring those very specific schools and that very specific spell should be the only way to increase the amount of physical/magical armor.
Resistances are applied before the armor takes damage. Increasing those resistances is, effectively, increasing your armor. However, it also gives you some benefit once your armor has broken.
In the current model, you sink some points into armor, maybe use spells to recover some of it the first time it breaks and then it breaks again in 1~2 turns based on how enemies decide to attack. Once your armor is gone, those points in physical/magical armor do nothing for you.
I also can't say for sure if fortify is the only spell that recovers/increases physical armor. Same goes for magic armor. All I know is that hydrosophist gives a bonus to magical armor recovery and increase while geomancy does the same for physical armor. Larian says they've added hundreds of new skills in DOS II and all we have right now is the intro map, there could be several more out there that come from schools other than hydrosophist and geomancy that recover/increase physical/magical armor.
