The problem are not the champions....
The problem are not the champions during this Season 6 but how imbalanced items are.
Riot introduced tons of new items this season without fully testing them and this created this unmanageable imbalance. The main issue with itemization right now are Tank Items. Tank items are extremely cheap, provide strong Unique Passive, AND MASSIVE health/resistances boost. This is why you see all mobile tanks dominate the game at the very moment.
However, this is not going to end because AP items are in the process of change.
The Imbalance will continue for a While.