The reason for tanks running rampant is not grasp

The real reason is how AP itemization is crap at the moment.

Here, have a look at some examples: http://champion.gg/champion/Poppy/Top http://champion.gg/champion/Amumu/Jungle http://champion.gg/champion/rammus

Tanks at the moment are free to build 4, or 5 armor items. This is because just single MR item grants them de facto immunity to magic damage - no mage is going to ever target a tank, no matter how low their MR, because they need all of their currently very limited resources to deal with users. In general nerfs to AP items made amount of magic damage available very low, a mage can't ever afford to hit the tank in a fight - it's too much of a waste.

So, mages won't target tanks because they are not able to, and AD champions obviously can't deal with 4 item armor tank as well - especially if that's Mal or Rammy. Grasp is part of the problem, but not the core of it - it's lack of balance between damage types that causes tanks to run freely. Rammy and others could always lane decently in some matchups - but in game balanced between magic and physical damage, when they couldn't actually get nigh-unkillable, giving them lane gold was a huge waste.

Above is also the reason why and are ones of very few damage-oriented mages that are strong ATM - they have natural tank-busting abilities, a tank who's only MR item is portal is Malza's wet dream.