The problem with MR and the case for Magic Armor

So with the changes to intellect giving Magic Resistance (MR) and the interaction of magic absorb with MR, as well as the plethora of sources of MR in the game, I think it's time to talk about how MR works.

Magic Resistance and Damage Mult

So how Magic resist works right now is that, against magic damage, the total Damage reduction stacks multiplicatively with each individual source of MR such that the damage multiplier (DM) is

DM = (1 - MR1) x (1 - MR2) x (1 - MR3) x ...

Which is less than 1 (i.e. reduces damage taken) The base MR is 25%. Adding 10% MR item gives
DM = (1-0.25) x (1-0.1) = 0.75 x 0.9 = 0.675.
This gives an effective MR
MReff = 1-DM = 0.325 or 32.5%

Effective Health

The above example would make it seem like stacking MR has diminishing returns. But oh contraire, because how damage mitigation works is that each additional % of MR is more valuable than the last. Let's define effective (magic) health.

Heff = H / DM = H / (1-MReff)

For baseline 25% MR, Heff = 4/3 * H or a 33.3% boost to effect (magic) health. Add an additional 10% MR, Heff = 10/9 * 4/3 * H for a total 48.1% boost to effective (magic) health, going up by 14.8% points. The 10% MR not only multiplies your raw health by 11%, but it's boosting the effectiveness of the 25% MR by 11%, so it scales exponentially. Add an additional 10% MR we get Heff = 10/9 * 10/9 * 4/3 * H for a 64.6% total boost to effective health, up by an additional 16.5%.

So adding more MR actually increases your effective health exponentially, each % of MR and each additional source of MR is more value than the last.

Also, having a single, large source of MR is better than multiple smaller sources, for example 5 10% MR sources vs 1 50% MR source,
Heff/H = (10/9 x 10/9 x 10/9 x 10/9 x 10/9) = 1.69 < 2

Exponential Growth

With the most recent update, for every 10 points of intellect we gain 1% MR to our base MR. As I will show, each % point of MR is more effective than the last. Compare baseline 25% MR and add 1% MR and see how much of a boost that 10 intellect provided to Heff.

Heff/H = 1.3333 for MR 25%
Heff/H = 1.3514 for MR 26%, or a 1.35% additional boost to Heff for 10 int

Now do the same when we're at 40% MR and add 1 % MR

Heff/H = 1.6667 for MR 40%
Heff/H = 1.6949 for MR 41% or a 1.69% additional boost to Heff for 10 int

I know it doesn't look like much, but the point is that it's also exponentially scaling. Every point of intellect gives you more effective (magic) health than the last point, and as the game goes later, every player's effective (magic) health grows exponentially. All the while, magic damage does not scale exponentially (or even linearly). Int allows you to cast more spells, and only some items directly increase your spell damage. Now this is by design, but the exponential growth of the defensive broadens the damage gap tremendously in the late game.

This is not the case with physical effective health and armor. The way that armor works is that each point of armor, whether from +armor items or from 6 agility, gives a consistent boost to effective health. The boost to effective health going from 15 armor to 16 armor is the same as going from 5 armor to 6, or about 6%. The exception is when you go into negative armor, but you can read more about armor scaling and effective health here

Conclusion

It might be time to add a form of magic armor to the game. One where each additional point of magic armor scales your effective (magic) health linearly just as with armor. This will make MR a much easier stat to balance with magic damage and make late-game magic builds at least a bit more viable without being out of control in the early-mid game. Or maybe what we have is fine as is, but it's at least important for players to understand how the scaling may impact the game in the late stages. Also just buy some MR dude it's really good, even better now.

Anyway, please feel free to correct me if I got any info wrong here and let me know what you think. I hope you all have a good day and a good dotes