Riot knows just how oppressive tank to win is.
There is without a doubt a certain annoyance into a full team of tanks. And not even just in normals or ranked. In pretty much every aspect of game modes. If there are more than three tanks it becomes extremely overly oppressive. Not just tank, more like juggernauts. If i deal with 
on the same team, it BECOMES extremely oppressive to even try to do anything. Walk this way, garen ults you, malph ults you and illaoi just yanks your soul away. Like why is that okay"? You dont see teams of assassins because it isnt overly oppressive, in fact it's a horrible decision because they cant delete a juggernaut quickly enough
