One of the most broken champions in the game, and the fact that she's immune to nerfs is hilarious.
Well, maybe she's not immune to nerfs, it's hard to tell because whenever Riot realises they can't get away with leaving the abomination that is Janna alone any longer, they tickle her and call it a day.
Anivia/Malz/TF/Karthus/Swain potentially too strong? Nerf them almost immediately, even if their playerbase is generally somewhat small.
Meanwhile Janna has to suffer losing .1 off her ult AP ratio, oh how it sucks to be her.
Whatever happened to clearly defined weaknesses?
Her lane phase is pretty good, those who say otherwise are typically basing "Oh she does nothing in lane" on the fact that your average Janna player who is just first timing her because she's broken freelo sits back and acts as a shield bot and stagnates the lane.
Her personal safety is beyond a joke, so "Oh she's squishy" means nothing.
It is impossible to play Assassins/pretty much every melee in the game against her, as she either kites them to oblivion or renders them useless in a manner that is very hard to counterplay.
You pretty much have to either be against a bad Janna or pick one of the few champions that can crush her in lane, while hoping that you don't have to suffer the inevitable camp that arises as a result of how aggressive you have to play to beat her.
She is disgusting. There are no valid arguments against rebalancing her.