When you have a bunch of individual sources of flat Physical Damage, (e.g., your weapon, your rings, your belt, etc.) they do not sum up before being evaluated against an enemy’s armor. Instead, Armor additively absorbs each source first, and then the results are summed together.
This wasn’t intentional and makes Physical much weaker than it looks on paper, but it’s how the game was balanced around so it’s not being fixed.
THAT’S WHY %DAMAGE IS SO MUCH BETTER ON WB EOR.
Now I get it. Holy shit. Thanks Ceno. You learn something new everyday.
To go offtangent a little because I’d like to know more about this…let’s use EoR as an example
x% WD + y flat phys on the base skill.
Do those 2 things count as “individual sources” too?
I believe so. I’m not 100% sure on whether buffs (Mog Pact) are treated as individual sources, though.
If this wasnt intentional, Crate could just remove enemy armour altogether. Why do they they leave it be then?
Because
Removing armor would give every Physical % Weapon Damage build in existence somewhere between a 20-40% damage amp. Not exactly a good idea.
So you mean to say that physical EoR is gimped by armor in 3 ways
In your opinion @Ceno, what does spellscourge need?
EDIT:
^What about lowering it
or you could just have spellscourge give your WD abilities a way to lower enemy armor. like -100%
A good question.
It depends on the direction Crate wants the set to stay. I, for one, do not like Blade Arc and even if it did a gazillion damage I’d probably still hate sets built around it ( I have never played Bloodrager… ), but I am not of the mind that adding Physical Damage to BA is the call (for various reasons, one of which you just learned. 
) Those small values of Physical Damage pale in comparison to what one could theoretically get out of BA’s % Weapon Damage; I say theoretically, however, because Spellscourge uniformly has godawful flat Weapon Damage on account of its shield and Arcanist/Soldier offering literally nothing in that regard.
DoT Spellscourge BA might be able to squeeze out some damage with new Overload, however if you’ve played much Spellscourge you’d know the set is not actually all that tanky and losing the ability to benefit from ADCTH on account of going DoT isn’t great.
Furthermore, Spellscourge does have the energy regen to sustain BA + Maiven’s, but not much else. Devastation is a massive load to add in to the mix and for not entirely much gain. Other utility spells and a movement rune (which is also unaffected by -%Cost) will quickly kill your energy pool.
What this all comes down to is that Spellscourge needs:
Given that that’s basically everything that every build needs, I’d personally argue that Spellscourge offers literally nothing to Battlemages and is not worth trying to build around. I don’t normally advocate for total overhauls (anymore), but the Soldier-side of Spellscourge sorely needs it.
If you had a place to put -% Armor, you’d also have a place to put -% RR. But we’re talking Battlemages, here. 
N Reduced Armor used to exist in the game but it was godawful (mostly because its values were too small (250ish range)) but Crate has since taken the stance not to reintroduce the stat.
Edit: Some ideas, just throwing them out there without many numbers:
Even with 100% elemental --> phys conversion?
It’s been awhile since I’ve tested spellscourge, but I recall in pre-FG, it was pretty damn tanky, what with aeon’s + transmuted overguard + mirror.
But that may no longer be the case, and the damage output wasn’t stellar
This I can attest to
What would be cool is if spellscourge was made into a 2H blade arc set for the battlemage. Bladearc is always a skill I’ve wanted to build around
You get some flat damage from IEE and that’s literally all the masteries give you. You could technically get some more from Menhir’s I guess, but the build has OA problems that necessitate Oleron’s imo.
Overguard isn’t what it was and Spellscourge no longer gives the Overguard support it once did.
I never understood how a battlemage could run into OA problems, but it’s real as fuck on this set, I’ll give you that.
#buffspellscourge2019
#buffFoI2019
Truth be told, I haven’t looked at its OA since Overload got some. The issue had always been not enough flat OA to make use of its buttload of % OA.
That and most of the gear generally tended toward defensiveness. Battlemage certainly misses the vanilla-release days of Clairvoyant Shoulders + Vestments of the Great Guardian.
The problem is still there. The build also suffers from a massive skill point insufficiency
P.S: @ceno - thanks for taking the time to explain all this to me. It’s much appreciated!
I tried Spellscourge recently, around 9 minutes in Crucible. Tanky, but not top tier defensively and damage is low. Investing in Devastation leads to energy issues. Set offer low DA and OA. I personally dump everything in cunning and reach like 3.1-3.2k OA. Oh and point hungry build.
Lot of things set lacks, RR is ofc the main problem.
And if you add the Spellscourge Set Devastation as a passive skill with a chance to work. Many sets have this, for example Targo with a hammer.
This will solve the cost problem of too many Ravage points.
And the Devastation bonuses are replaced by OFF. Which will solve the problem with RR.
This completely fits into the concept of the AOE-damager.
No thank you. Please leave OFF out of this. You’d need to have HUGE amounts of -X% freeze res to enemies for OFF to be a viable late game skill.
Changing devastation to a proc is okay I guess, if and only if there’s a solid skill modifier to it.
Adding insult to injury on the Armour bug. I remember it was discovered long after Armour reduction was removed from player skills as everyone believed it was useless.
I wonder if it would be more impactful now at enabling builds designed around small but frequent sources of Physical damage.
it would be probably. add N (N=100…300…500) reduced armor to Devastation base skill, and another 1000 on the spellscourge set (assuming mechanic works). This leaves 500 to be added to a stopgap item skill modifier. (Like a faction / MI medal)
Does Discord-Cadence have anything to give to a BaMa?
Still runs the problem of lacking resist reduction from either mastery forcing you to try and scrape as much together from gear.