How riot can think tanks are ok?

I think riot can't undestand his own game. There is no balance in tanks. You can dodge every single spell of them, they still win the fight or survive. They can missplay 5 times in a row without any consequences. But in this game ppl are capable of missplaying 20 times in a row. Well now the enemy poppy is 0/5/0 , 4k diff, still she is unkillable and deal very high dmg building 2 tanks items. In wich world is this a fair or balanced thing? This what happend last game, i was yasuo top, send her 0/5 cause she was so fucking bad. In the meantime the enemy amumu is 0/3/0 and my panth jungle is 5/0/0. Easy game for us? No we lost every single teamfight cause they where unkillable anyway, they had infinite cc chain and enough dmg to carry game. Exactly a 0/5/0 poppy and a 0/3/0 amumu carried the fucking game..... Is this champ gap or what else?