This seems a little backwards.
Irelia comes out, and not only is she hotfix nerfed, she's nerfed again next patch. What's her winrate? Oh, between 48 and 49%. She struggles in lane and can hardly fight most tops and mids early, and only comes into her own late game.
Kai'sa comes out, she gets hotfix buffed, and then buffed again. What's her winrate? Oh, 54%? Not one nerf slated for her, despite having a 20% pickrate and a 54% winrate (meaning she's literally freelo, but hey).
See, thing is, Irelia has a higher skillcap now, and whales can't play her. Not only that, but she can actually compete with ADCs late game, and that's not allowed. So she's being nerfed repeatedly to prevent that. Kai'sa, on the other hand, is braindead and an ADC, so whales love her -- which means Riot does too.
Isn't F2P neat? So glad it's a popular thing now.
"You can't milk those!"
. 