Thanks for the responses! I should point out I'm not saying I think there's anything wrong with the system - just that I don't really understand it.
So originally in RoC there was no magic damage, piercing did extra to heavy armour and medium had no bonuses or maluses so piercing damage and casters were kinda broken. To rebalance this they added magic damage and changed up the damage tables.
I think I was too young and foolish to really engage with it on an intellectual level at the time, but I do vaguely remember it. If I recall correctly, the armour types were distributed between units differently as well. Maybe a lot of the units that have heavy armour now used to have medium or something? I'm not sure.
The damage and weapon types work better mechanically than being accurate thematically. For example, most base units like ghouls and grunts etc have heavy armour so they aren't too weak early game and aren't hard countered by say Archers or Riflemen for example.
Yeah, I've realised in a lot of cases it seems more like a unit classification than anything to do with their actual armour - something like: heavy corresponds to melee unit, medium to ranged ground units, light to flying units and unarmoured to spellcasters. And thinking about it that way it seems to make more sense, but then there are quite a few exceptions.
Spellbreakers only have Heavy armour in the campaign, in multiplayer they have medium, if they had heavy they'd be OP and broken. Also whilst magic damage on most units is very low they deal 200% damage to Heavy or 2x damage, so 10-11 magic damage becomes 20-22 negating armour penalties which is pretty good considering.
Interesting. I've mostly played the campaigns and only a bit of multiplayer, not enough to notice that there was anything different. I guess that also means the World Editor uses the campaign balance, since that says Spellbreakers have heavy armour.
Siege damage is pretty rare in multiplayer, so Fortified armour is pretty good, Orc burrows need the upgrade to provide a weakness in certain match-ups a common Human strat is to rush in a good amount of Footman and aim down the Orc burrows to supply block them.
Yeah, I understand that Fortified armour is usually better (i.e. against anything that isn't siege damage) so it is generally an upgrade. I just find it strange that some upgrades can actually end up being worse in some situations. Also, it sounds like you're saying Burrows have heavy armour to enable humans to use a silly cheese strategy.
As is often the case in computer games, realism is sacrificed for the sake of gameplay. Balance and diversity of strategies explains all the examples you listed: ghouls and tauren both need heavy armor to be durable melee in their respective tiers; spell breakers I remember the patch notes in which their armor type was changed to medium, and the pointed reason was they were too tanky because of heavy armor and excellent synergy with other arcane sanctum units; mountain giants are supposed to be very durable but not invencible, therefore they have medium armor so melee works against them.
I understand what you're saying, but this sort of feels backwards to me. Heavy armour only makes units durable in melee because the designers made it that way. They could easily have picked a different armour type for that (and indeed, it was medium that was like that originally).
But I suppose once they'd decided that (say) Tauren and Knights would interact with damage in the same way, and that damage interactions were determined by something called "armour type", the mechanics were never going to match the visuals.
Other RTS games I'm familiar with don't seem to have this issue somehow. (Although that said, in Age of Empires II, camels were classified as ships for 20 years...)
To me, the only intriguing case is the huntress, as unarmored does make her very squishy, but they all have a logic to it.
Yes, somehow this is the weirdest one to me (except maybe the thing with Corrosive Breath). I have a vague recollection that they had a different armour type when The Frozen Throne was new, and it got changed shortly after release - but I could be misremembering.
