Cassiopeia is a shadow of her former self
Her twin fang nerfs were one thing, but now that Phase Rush is incredibly weak early compared to Stormraider's Surge her laning is abysmally bad compared to what it used to be. She isn't able to out damage or out maneuver laning opponents anymore now that everyone can take celerity, and Phase Rush will never have even close to the level of impact that Stormraider's did during her lane.
We're talking about a champion with no innate defenses besides miasma(which has a minimum cast range) and a situationally hard to land ult that can be easily outplayed. Cassiopeia has no 2 second Ryze root, or Azir dash/shield, or AoE Syndra stun, or Orianna shields.... her lane identity was always supposed to be a dangerous machine gun damage mage that could melt faces if she played her ranges perfectly in lane but was food if you jumped on her, but right now she just feels like a limp noodle and gets out traded by every other mid laner except Ryze.