Patch 7.20 introduced a big change to a fundamental mechanic of Dota 2, and from our experience players still haven’t fully adjusted to it. We're taking a deep look into the changes to armor calculations and what it means for the players.
Armor is now more effective across the board. The formula for calculating physical damage resistance was changed from (0.05 × armor) ÷ (1 + 0.05 × |armor|) to ( 0.052 * armor ) ÷ ( 0.9 + 0.048 * |armor|).
The changes already becomes substantial at 10 armor, with an almost 4.5% less physical damage taken under the new rules of the game. In a game where heroes often reach 30+ armor it can make a huge difference: most of the damage dealt in the late game is physical and when carry heroes start hitting for 300+ damage with potential critical hits, these increments quickly start adding up.
It should be clear from the table that stacking armor provides diminishing returns. While the first point in armor raises your overall physical resistance by 5.49%, the fifth point only increases it by 3.76%. Every point of armor after the 27th will give you less than 1% of extra physical resistance. There is still truth to the idea that every point of armor gives you ~5% extra EHP against physical damage, but the effectiveness of this EHP is still diminished.
It means that there is what we will refer to as "high value armor" and "low value armor". For simplicity, we will consider anything below 20 armor "high value armor" and extra points of armor above 20 "low value armor".
Armor reduction effects is when it comes into play as a major factor for DPS calculations. Armor is a multiplicative effect, so armor reduction scales pretty efficiently into the late game and can be devastating in the midgame. Desolator was perhaps one of the most underrated items, and we can already see how professional players are adapting to the new patch in the Chongqing Major qualifiers. The new armor formula is also part of the reason heroes like Dazzle and Phantom Assassin are incredibly popular and why both heroes had to be nerfed shortly after the patch 7.20 changes.
By cutting into "high value armor" through armor reduction effects you can greatly increase the amount of damage you deal from auto-attacks. For a target with 25 armor there is an almost 9% multiplier difference between an attack with and without Desolator effect, and that is only cutting into two points of "high value armor". For a target with 20 armor the multiplier difference becomes 11.55%. It is 15.75% for a target with 15 armor and a whopping 22.74% for a target with 10 armor.
Assuming you are a Phantom Assassin at level 12 with an average crit of 750 damage, you would effectively deal 68, 87, 119 and 170 more actual damage. As you can see, these values are far from trivial, especially when it comes to quickly disposing of enemy supports with low armor—you are cutting into the "highest value armor". The extra physical damage you deal on targets with negative armor can also get out of hand pretty quickly. In fact, after the patch changes, getting enemy heroes into the negative armor range might once again become a strategy.
This leads us to several conclusions. Armor auras are amazing for helping your supports survive and it is the reason we often see items like Vladmir's Offering being built on cores or position four supports. In the beginning of the game these extra points of "high value armor" provide a lot of sustain. Small armor bonuses from Buckler and Mekansm can also play a major role in the outcome of the teamfights. Finally, Assault Cuirass is still pretty underrated for the benefits it provides.
Towers are much easier to destroy. Our initial impression during the general changes analysis was that the effects of extra HP and reduced armor of increased effectiveness would cancel each other out. We were wrong—while in vacuum the EHP of towers is more or less the same, when we take into account the armor reduction abilities the situation drastically changes. Once again, you will be cutting the the "high value armor"—even Tier 4 towers now have only 21 armor. You can easily reduce this value by 7 or 12 points, gaining ~11% or even ~22% effective damage from your physical attacks.
There is also still little point in trying to chip-reduce armor of targets with exceptional armor ratings, such as currently popular Morphling and Terrorblade. The latter has 32 natural armor at level 25 without any items or talents. Even when critting for some crazy value of 1.5k damage, the difference Desolator would make is less than a 100 damage. Against targets like this you either have to go all in, with heroes like Elder Titan or a really well-played Dazzle, or just find some other solutions. All conventional armor reductions sources on such targets will cut into "low value armor" and are not worth the effort.
Finally, cleave, which is now reduced by armor, is also in an interesting place. To compensate for physical damage reduction, the cleave values on Great Cleave, Empower and Tidebringer were changed. The former got completely destroyed, with a minimal increase to its effectiveness, and is more or less only useful for farming low-armor creeps. Both Empower and Tidebringer, however, were buffed quite substantially. Currently, Kunkka actually deals more cleave damage from Tidebringer on targets that resist less than ~40% of physical damage, meaning that as long as your cleave targets have 11 armor or less, you can expect to deal at least the same amount of damage as previously. It also means that armor reduction on backline targets can yield even crazier results than previously.
Dota mechanics are always an interesting topic to discuss, since they can fundamentally change how we approach the game. With the increase of armor effectiveness, the overall survivability of heroes should theoretically increase. At least when it comes to physical damage.
At the same time, there are now slightly more sources of spell amplification—perhaps going forward we will actually see more magic damage dealing cores and magic damage lineups will become more relevant in the later stages of the game. We've seen glimpses of it happening previously, so do keep an open mind for the next couple of months—Dota is still full of surprises.