Another huge disparity: MR is strong vs AP champs, armor is useless vs AD champs
When facing multiple AP champs the decision what to build is pretty easy taken. Both Banshee and Spirit Visage offer both HP and MR. When facing AD champs the decision becomes unclear. Most AD champs don't care about armor or when they do they can buy items to deal magic damage on hit or they have other means to get pass your armor. Also they can buy crit or they are AS based champs. So wether you buy armor, hp or AS reduction it is never enough while mr and hp simply counter mages. Lets take a look.
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Champs
: magic damage on hit on his ult
Hybrid scaling
Hybrid scaling
True damage
Activates W to ignore all enemy armor
Barrel armor penetration basically means true damage
True HP% damage
Magic+ max HP% damage on every 3rd hit
magic damage on hit
Activates E so bBasic attacks deal bonus true damage on hit
Activates E to deal true damage to target enemy
Huge amount of magic damage. You can even build him AP and delete squishies just by pressing W
Hybryd
Steals your armor and mr with his ult
Hybryd
True HP% damage
50% armor penetration on his ult -
Items AD/AS based champs can buy
Turns your HP into bonus (at least) physical damage
tons of magic damage on hit
tons of magic damage on hit
Turns your HP into bonus (at least) physical damage
tons of magic damage on hit
tons of magic damage on hit -
**Compared to AD/AS champs no single mage deals bonus physical damage on hit! Just a couple deal HP% damage and mostly missing HP% magic damage. **
Max HP% magic damage. Very low scaling
Only AP champ with truely an nti-tank ablity in his kit. His pool deals Max% magic damage but recently got nerfed andnow deals 25% less damage at max stacks
Only AP champ with true damage in his kit
is the only AP item that deals HP based damage but it sucks compared to the AD items based on HP damage and to most AD/AS champ's kit to deal with HP stacking champs.
- Conclusion So basically you build MR and HP and almost every AP champ is countered and both stats are available on the same items. When you build armor vs AD champs they have tools to deal magic damage to you or damage based on your HP. AS based champs will start ignoring your armor by dealing magic damage on hit or start ignoring your armor because they have abilities like Fiora, Vayne, Irelia. Therefor the following items make no sense:
This should be vs AD champs reliant on criticals and champs reliant on HP% physical damage
This should be vs AS champs, but they usually deal tons of magic damage on hit or have other ways to bypass your armor so this item should give MR instead of armor
This shoud be vs AS reliant champs who deal mostly physical damage and HP% physical damage.
TL;DR: At this point armor is the most useless stat in the game and AS reduction feels the most unsatisfactory stat to build since it comes with armor while you really need MR. Also why do so many AD champs have items or abilities to nullify armor/HP while AP champs don't have the same options? AD champs can buy items to deal massive magic damage on hit to render armor useless but AP champs don't have items to deal physical damage on hit.

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