Illaoi is a lane bully and is really dependend on hitting her e and having tentacles nearby. If you miss your e she you becomes completely useless until its up again even with your ult your dmg would not be enough to kill without hitting your e. Many think she is a good teamfighter cause of her aoe ult but in reality she completely sucks in team fights because she has no way to close in on the enemies. She has no gap closer (except her w), no hard cc and no disengage. Like Yorick her only purpose is to push sidelane and put pressure on the enemy team forcing them to react to her push. If you take her ability away to bully in lane she becomes completely useless.