Kai'sa Shield VS Vayne Stealth
Kai'sa is literally the only ADC with a shield in her base kit, unless you count Urgot, but everyone knows he's far from an ADC.
Now, let's compare her to a similar champ--Vayne. Let's look at differences in their big mobility ults--Vayne has invisibility, making it HARDER TO DO DAMAGE, while Kai'sa gets a BIGASS SHIELD, making it IMPOSSIBLE TO DO DAMAGE. I've seen Kai'sa ults not for repositioning, not for dodging a skillshot, but for the shield alone when they're about to lose a fight. Yeah, a Vayne might use her ult to escape a bad situation, but having a skillshot that gives stealth and can be predicted by an opponent's skillshot definitely requires more skill than "oh shit, boutta die!" and pressing R on Kai'sa.
I just feel like, while Kai'sa's long-ranged dash is a cool mobility tool that allows for amazing counterplay, the shield is the exact opposite.