Not only is Darius E already lowering the value of Conqueror's and his R is already true damage, Black Cleaver is even furthering that. You literally have half the damage amplification you would get with another champion from Conqueror's if you go that route. You should probably go Trinity Force (+Steraks I guess) if you wanna go Conqueror's.
Except you're math is wrong.
Darius is an anti tank champ. A tank with 200 armor is still going to have ~100 armor even after BC/E.
100 Armor is 50% phys damage reduction. If you were going to deal 1000 damage on a trade before armor without Conqueors you'd deal 500... with it 600. That'snot even including the flat AD you get out of it will will add another 40 or so damage. No other Keystone is going to add that much vs a tank.
Armor pen gets MORE powerful as you stack it. Not less. Obviously the same works with True damage. Darious makes use of % armor reduction... not flat armor reduction. Thus True damage even notably increases his damage vs squishies. An ADC with a GA with ~ 100 armor late game still has 50 armor AFTER fulling stacking BC. Because Darius doesn't build Flat ARP that would take the same 1000 damage (simply using for easy math) from ~650-700(including stack time) to more like 800+. You could make an argument that something like Electrocute is better singletarget/burst damage... but well this is Darius.. he's going to keep that damage bonus as long as he stays in the fight.
Also BC takes a while to stack, it isn't instant. It takes 3-4 seconds to stack. Conqueror's true damage is going to be applied instantly simply from being in combat from minions. Also Darius doesn't START the game with 5 ranks in E and a BC. He's not going to have that ARP before a tank has already built Tabis + armor item. Around level 9 or 10. Hell your average solo queue game is pretty much decided by then sadly.
Also the true damage ulti isn't even part of the equation really. By that logic BC is also a bad item.
Hell the entire point of Darius is getting someone inside of ulti execute range. He's also a champion that excels at turning around 2v1 ganks vs a tanky laner. More AD and True damage will make that happen more often.
i don't take conqueror on darius
way too inferior to phase rush because darius has true damage and E passive
the permanent move speed from bleed is still valuable
However not every target is hit by E, and BC isn't fully stacked for the entirely of any given trade.
Conqueror is still the highest damage Darius Keystone for any multi target fight. Obviously phase rush is better for comps that don't have enough lockdown for Darius to get on targets.
What if you want be friendly and lower people's armor for your friends?
