Nobody can argue that this is the best ADC in the game and has been since her release. Sitting now at a 40% pick rate with just under a 50% win rate. The last 2 champions to reach this status were Kalista and Lucian who both got demolished accordingly with nerfs. So when do we get Kai'sa nerfs? I am tired of seeing this champion nearly ever game because she is just too good at everything.
IMO her passive is too strong.
Its ... kind of just how ADCs are.
if there's no strong reason not to, ADC players don't migrate champions very often. There's no playstyle or niche diversity, and Kaisa's design just makes her good.
Even if you strip the shield from her R, raise the gate on her E invis and nerf the passive, she's still going to provide high physical AoE damage and good % max hp damage and have a mini-Ez Ulti. She's like Ezreal and Vayne but without either's primary drawback of a lack of waveclear, and scales just as hard.
That said as long as Lucian, Twitch, Jinx, and the aforementioned Ez/Vayne exist in their current state there's at least reason to not pick her but the choice is pretty much moot as they all have the same job and the same path to accomplish it.
u know, kai'sa might be good, but she's so squishy it's disgusting. i get 2 shots by a jhin who only has 
, caitlin demolish her with every crit she does and the strongest point isn't about having a strong champ. if your teammates are really bad or your support can't even land a hit on something even the minions than your game's fucked. kai'sa in higher rank might be a strong champ, but she depends a lot on her team early, that's why she's trash in silver and above, limit in gold even.
before she gets nerfed, they'll nerf jhin's passive and jinx's attack speed ^^'
