I remind you that sometimes a champion is OP because of meta shifts.
I am not saying this in response to anything right now, but i was reminded of the hate for trundle a few months ago where people screamed about him being OP. He was definitely performing above average but if riot were to nerf him, once the meta shifted a bit he would be underpowered and he would have to be buffed again. Sometimes its just better to wait a bit when it comes to buffing and nerfing a champion. EDIT: better example. 58% winrate rammus after the ADC update.

nerfs after devourer was removed

Both got kicked in the nuts for jungle updates. Twice.
against him, and force him to blow ult on mini-gnar to survive fights if you can. He barely gains tank stats, you transform, and suddenly your stats overwhelm his by massive margins. You also have consistent poke, a nice HP chunking passive on W forcing him to keep farming or he dies, and your mini E or mega E can fly over his pillar, allowing for quick escapes, and in mega Gnar you have enough CC to stall him from reaching the team even IF he ults you to attack.
While he still was annoying and a threat to many champions im pretty sure he wasn't called op by every body until bruiser yas showed up