Why is Akali allowed to be this strong?

I thought that Riot wants the game to be fun whether the champ you are playing or the champ you are playing against. Akali is definitely not "fun" to play against. Her Q auto, gunblade, and passive heals her all the way to half health. The worst part about her is her being super low health and she zhonyas and you think you're about to kill her but, nope she just jumped up to half health and now you're dead. She can instantly burst anyone and still heal most of her health to get out.