There's so many problems with balancing right now
It's not one or a couple champs. It's honestly the combination of all the new items, changed items, new champions, champ changes, along with class overhaul.
There are so many items now with unique passives that are very unique. Like
+
together is really strong.
gives high attack speed, high cooldown reduction, large movement speed buff, and high flat damage. Then there's the obnoxious healing of
, tankiness of
and
.
If you had those 6 items I just mentioned in a single build you'd have 4000+ health and do a shit ton of damage and be immune to burst, while being able to kite and chase.
Core AP items now gives CDR
paired with the tankiness of

GA is super cheap now because of all the other items being so good, which makes GA a cheap and good buy
Then there's overloaded champs like
along with just the usually imbalance of the game
Then there's the flat dmg of fervor ~120 per auto attack without a single item
It's the combination of all these things that are making the game unbalanced, unfun, and repetitive.
these items are almost never used anymore unless it's a specific counter item. The game needs some big changes if any of the problems being complained about are to be fixed.
and 
(That you never see an ADC with) and
(which feels like it should switch passives with 

with