After some pure AA(IE), pure AS (Hurrican), pure AR(Thornmail), almost pure health(Warmog), pure AP (Rabahan), it feels really weird that we dont have a super MR item to counter the AP carries quickly when they pick up a triple or a quadra accidentally in the last team fight. Such item can allow us to delay the core item for a better mid game or to round of your tank build at late game (pretty much the way the current thornmail works).
And it is worth mention that by have such a small variety of MR item, Ohmwrecker also become kinda useless --------- if you are likely to have some much AR item as the core item, why would it ever be meaningful to build sth to deal with the turret specifically? It is happy to see that S3 provide us item so that we no longer struggle how to turret dive effectively, but it is not happy that it is now even tougher for the tanks to build against heavy magic dmg, considering how tough it was to build 200MR and how even tougher for you build it(even you take it down to 180 to balance off the global stat nerf).