Let's talk magic penetration and Tanks

+ + ++standard health stacking items =no mage can touch me

At the moment, mages lack any real answer to this. For you see, what seperates mages from AD based champions, is that AD based champions despite what people say, are pretty good at killing tanks. The reason for this, is largely because, AD based champions are capable of relying on 2 forms of damage. Casting spells/abilities and auto attacks while many of them having passive abilities to help them kill tanks faster. W passive her entire fucking kit is designed to kill tanks Ultimate and crit based true damage 4th shot his everything. Now this isn't necessary about "are these champions great killing tanks" this is more so about, they can handle tanks better than mages, for they have more than 1 way to deal damage. A mage however, and even AP assassins are hard core destroyed by a team that is mostly made up of tanks. The large reason for this is because, unlike their AD counter parts who can rely on both autos and spells, a mage can only rely on a spell combo rotation. So if some baddie on the enemy team is stacking magic resist items and health, a mage will do quite laughable damage to said person. The easiest solution an AP champion has for this? Well, simply get fed before the tank does. (far easier said than done)

Now frankly this is caused by 1 major thing, while build diversity has improved on mages vs what it use to be a year or so ago, it still has yet to improve to the level it could be at.

are the only magic penetration items in the game while can realisticly only be bought by tanks or supoprts or as a late game defensive item for mages if they feel they need one

Now let us look at the options AD counter parts have. For the sake of saving time and to avoid debates, I will be focusing on the counter parts of mages, assasins and fighters.

Now I know what people say, and yes it's true, Lethality is better for killing squishy targets. However..to say if a Zed who has the following build.

BUILD:

To say that the 36 Lethality at level 18 wasn't doing any work to help him kill , would be a lie. Infact at this point unless the maoki was stacking every armor item in the game onto himself, the zed should be able to handle the maoki now in a one v one scenario just fine. Now zed is also not the only person who can go this build. are all capable of building simmiliar and it DOES help a lot. (key word simmiliar, i'm aware each champ has his or her own needs and situatinos on each game ask for their own build)

Granted though the difference was assassins and fighters really needed these items, for it was getting to the point they were useless champions for they would just fall off so hard, so fast. Which is what brought the demand for Riot to invent more options. Now what made the difference here is that lethality also helped these characters be good at fighting both squishies and tanks, and it took a while for Riot to find a math formula they were satisfied with that pleased both us and them in terms of balance. However mages can easily avoid this problem

Mages also differ though in the sense that mages have and always will be in many metas a very viable class, but the issue stands, that tanks simply destroy mages, and mages are in need of build variety options to handle it. One of the major joys that items provide to this game is to give players a way to problem solve difficult situations. If scenario A is happening than what is the most optimal solution in how to solve it? Items help give you answers, they add to that problem solving equation Which is why, an item that focuses on shredding magic resist while doing lack luster damage to squishies, would be so very helpful for mages while giving them a choice.

"do i want to nuke the adc, or do i want to shred the tank?"