On the context of the Urgot rework

"We do not rework champions because they are weak or unpopular. We rework champions because they are bad for the game" -ZenonTheStoic

In that case

literally makes top lane revolve around him and teaches players that if you ignore all interaction from the rest of the team and afk farm for twenty minutes, you will be rewarded with God Tier duelling and pushing power.

If you can't win the game in under ten minutes, doesn't matter if she's been farming under turret with no kills, she's going to be 1v5ing the entire team sooner or later.

Beat her in lane? No problem. She'll be roaming faster then anyone in the game and all inning squishies with zero counter play mid game. Late game her mobility is doubled again.

In a game where skill shots are the new direction for counter play friendly games, Kalista's entire kit -is- free counter play.

The ability to get kills all the way across the map without clicking a button in the last five minutes.

none of these champions are particularly OP, they have weaknesses, but they make the game so very unfun for the opponent.

I could go on. Dodging a corrosive charge and all inning one of the slowest adc's in the game is not the hardest thing to do, and mages naturally stomp on urgot because of his tendency to build armor. Maybe it's because Urgot can actually fight Riven that he's being deemed toxic to the game?