Even though the siege system is getting an overhaul, there's something about the overpoweredness of the Arrow Towers I'd like to point out. I'm not sure if this is a bug or intentional, but I still find it a very... peculiar balance design.
Here are the armor levels for cavalry in Edain:
Armor EdainCavalryArmor
Armor = DEFAULT 100%
Armor = SLASH 30%
Armor = PIERCE 100%
Armor = CAVALRY_RANGED 100%
Armor = SPECIALIST 135%
Armor = CRUSH 100%
Armor = CAVALRY 100%
Armor = SIEGE 100%
Armor = FLAME 100%
Armor = FROST 100%
Armor = MAGIC 100%
Armor = HERO 100%
Armor = HERO_RANGED 100%
Armor = STRUCTURAL 135%
Armor = CHOP 45%
Armor = URUK 30%
Armor = WATER 135%
FlankedPenalty = 12%
End
The higher the number, the more Cavalry takes damage. For example, they take only 30% damage from swords (Slash), but 135% damage from pikes (Specialist). Note that they take 135% damage from Structural, which refers to Arrow Towers, level 2 Defensive Measurements and other structure-based defences. This is already quite a large number, meaning Arrow Towers wreck Cavalry. However, let's take a look at Cavalry with Heavy Armor:
Armor EdainCavalryHeavyArmor
Armor = DEFAULT 100%
Armor = SLASH 30%
Armor = PIERCE 65%
Armor = CAVALRY_RANGED 135%
Armor = SPECIALIST 135%
Armor = CRUSH 100%
Armor = CAVALRY 100%
Armor = SIEGE 100%
Armor = FLAME 100%
Armor = FROST 100%
Armor = MAGIC 100%
Armor = HERO 150%
Armor = HERO_RANGED 150%
Armor = STRUCTURAL 200%
Armor = CHOP 30%
Armor = URUK 45%
Armor = WATER 135%
FlankedPenalty = 12%
End
Note how Structural does 200% damage now. This means Arrow Towers deal 1.5x more damage to Cavalry after you upgrade them with Heavy Armor, so upgrading your Cavalry makes them even more susceptible to base defences. This is not the only case, though. EdainInfantryArmor takes 100% damage from Structural weapons, while EdainInfantryHeavyArmor takes 150% damage. Same for EdainPikemanArmor and EdainPikemanHeavyArmor. The same applies to EdainTrollArmor and EdainTrollHeavyArmor. For EdainArcherArmor and EdainArcherHeavyArmor, the numbers are 50% and 75%, respectively.
If you upgrade a unit's armor, why make the unit more vulnerable? I can somewhat understand why Cavalry_Ranged, Hero and Hero_Ranged have been increased, as those unit types are reasonably rare, and can be considered specialized in taking out heavily armored units, but base defences are way too easy to spam. With the current system, only Battering Rams (1% damage from Structural), Catapults and their equivalents (1% damage from Structural), and Heroes (25%-35% damage from Structural, 15%-25% damage with armor upgrades) take reasonably low damage from Catapults, so when you're assaulting a fully towered enemy base, you're better off sending your Cavalry, Swordsmen and Pikes elsewhere, and have Heroes and maybe Archers support your siege equipment, or otherwise your army, to which you spent lots of resources to upgrade, will be hopelessly massacred.
Even if there will be new siege units, I can't really consider this kind of balance design very strategic, as it reinforces that you switch your late-game to practically one unit type, which is siege (well, combined with heroes as cannon fodder). In the vanilla game, upgrading units with Heavy Armor made them take 1/3-2/3 of the damage they'd normally take from Structural type weapons. Even in Edain 3.8.1, upgrading with Heavy Armor made the units take 0.75x of their original Structural damage. I'd really hope that the Structural damage for units with Heavy Armor upgrade will be reduced to the levels they were in 3.8.1, so that you can successfully mix both siege and your army to assault an enemy base. For Rohan, this is almost impossible on a Castle map, since a) their Onagers deal pitiful damage, and b) all of their other non-hero units (especially Cavalry, which is Rohan's trademark) get wrecked by defences.