I feel that the balance is off between magic damage, and magic resist. I know that AP does not equal magic power, but it can come pretty close on some champions. It is really hard to get to 300 magic resist, and it is not so uncommon for champions to deal 300+ magic damage.
Because I totally loved being invalidated by Rammus in season 2 with FoN alone.
MR is fine. I wouldn't object to a new MR item (that isn't HURR DURR 76 RESISTANCE FK U MAGE SCUM), or rework Banshee's to be an active.
AP tends to be more bursty, rather than sustained, so there's less MR total. It makes it so mages and other AP champions have a better early/mid game (while the adc tends to have the best late-game). It's part of why the popular MR items (spirit visage, banshee's) give health as well, making them somewhat useful against AD champions instead of useless as well as the fact that Liandries isn't as popular or powerful as Botrk is.
Armor and MR can be thought of as % effective health. 100 MR will cut magic damage in half and 200 will reduce it to a third.
Thus giving you 200 and 300% effective health against magic damage.
Most magic damage however comes in the form of burst. Doing a lot of damage quickly, but not so much over time. It's important to note A good chunk of AP Burst Can be mitigated, though Item utility rather than just strait up stats. Items like Zonya's and Banshee's veil. Their also tend to be fewer magic threats than Physical ones. (like towers)
And that's part of the reason why their isn't huge amounts of MR stacking. They don't need it. It's only really lame against certain AP DPS champs like Rumble, Vlad and Cass.
Not sure if you're joking or trolling or don't get how the stats work. Points in Armor or Magic Rez give a bonus % reduction to the flat AP or AD damages. 300 AP on a mage may mean 150-250 damage, that then gets split by usually around 50% due to resists, or more if you're tanky.
Like what others said. Armor and MR isn't just subtracting damage. It's reducing by percentage. For example, if you have 100 armor, then you have 200% effective health, which means that physical damage will do 50% damage to you. If you have 200 MR, then you have 300% effective health, which means that magical damage is 66% reduced.
Thank you every one who pointed out that MR is a %, you all get bonus points. Now that everyone got that off their chest we can talk about the real problem. Namely that we could use a little wider selection of MR items. For instance when your team starts losing a lane if it is to a AD heavy champion you can buy Frozen Heart, or Thornmail, and be just fine. However with some champions there is not enough MR in the shop to make much of a difference.
