For me it is kinda surpraising that a tank stat line is missing for the champions. I mean, we have values for cc and scaleing and stuff, but no stat for how good a certain champ is when he builds tanky. At the moment it depends on the role you are playing how effective tankiness is on a champ a player plays. In my opinion not only the role should determine how effective tankiness is on any given champ but also a champ. Gangplank just isn`t as good of a tank as Malph and Annie not nearly as good as a tank supp as Alli. Hope my point came across :)
