The Problem With Lethality...?
Doing a bit of digging, and reading up on Armor as a foundational mechanic. Whereas it does not function as damage reduction, it actually calculates as Effective Health. (It's vaguely complicated... if you have 60 armor and 1000 hp, you have to take 1600 physical damage before you die.) Now then. This is a problematic calculation, as opposed to a direct damage reduction, and I will explain why.
Given 30 flat armor reduction and 30% armor reduction, and the target is affected by 10 flat armor penetration and 45% bonus armor penetration,
- Target A has 300 armor (100 base and 200 bonus armor).
- The 300 is reduced to 270 (90 base and 180 bonus armor) by the 30 armor reduction.
- The 270 is reduced to 189 (63 base and 126 bonus armor) by the 30% armor reduction.
- The 189 is considered to be 132.3 (63 base and 69.3 bonus armor) by the 45% bonus armor penetration.
- The 132.3 is considered to be 122.3 by the 10 armor penetration.
- Target A takes damage as if it has 122.3 armor.
The above is from the Wiki concerning how Armor Penetration works, and what order this is calculated in.
Taking these two facts, let us simply bump the 60 armor to 100... thus 100 Armor, and say 2000 hp as this is more viable to the discussion. At 100 armor the incoming physical damage is reduced by 50%, and you gain 100% of the effective health... again, this means that you have to take 4000 physical damage (after the 50% reduction) before you die. (Yes, you gain 1% effective health for every point of armor, at 100 armor you are gaining 100% of your health as effective health.)
Let us take two items that are fairly common a LW and Duskblade.
Your armor now does something fairly interesting, as it did above.
100 - 35% = 65 65 - 18 = 47
This is where it becomes problematic. The Damage Reduction armor calculation is run each time damage is incoming. This means that now the algorithm is negating you down to 47 armor, and running the calculation once again with each attack...
2000 health with 47 armor = 2,940 Effective Health, 35% Reduction (rounded). (You had 4000 Effective Health, 50% reduction.)
What does this mean?
- Before these two items, let us say that the ADC was critting you for 300 damage, meaning their pre-armor hit would have been 600 damage. (It takes 13 shots to kill you).
- Their Crits should now be hitting you for 390, if all that had actually happened was that the damage reduction was reduced... however that is not what happened. Your 'Effective Health' has also fallen, by a vast degree, and is not negating damage. (It should take 10 shots to kill you)
- A 26.5% drop has also happened to your effective health... You are being hit for 549 damage. (It now only requires 5 shots to kill you.)
What we see, by running the algorithms that RIOT says that it uses (with a very small bit of rounding for ease of reading), 35% Armor Penetration effectively increases damage far more than 35%. While it is PENETRATING 35% of your armor, the actual damage gain is far higher.
The meaning?
ADCs blow massive holes in tanks, with the purchase of 1-2 items, effectively negating their ability to tank using armor at all.
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