When you realize a perfectly balanced champion was only nerfed for worlds
wasn't even sitting at a 50% average win rate before her changes. If you actually look at the graph of her win rate over the course of game length her mid game was already really slacking compared to her early game and late game.
I admit that Orianna and Syndra are both very strong maybe even OP but Cassiopeia was really a balanced champion that also happened to be viable. Out of all the popular mid lane picks, she was the one that was actually balanced unlike Corki, Syndra, Orianna, and Gallio.
Seriously Riot consider your approach to improving mid lane diversity other than "ooh lets just nerf all the popular comfort picks and hope they decide to lock in other picks for worlds" because we already know they are still gonna resort to their comfort picks. Buffing AP assassins isn't going to change anything either,