Why some champions nerfed the exact second they get played in the pro scene?

Early season 4, and are god tier. Both get nerfed into the ground. Later Kha'Zix gets a 10 damage buff on his Q and during the end of the Summer split and worlds gets some play. He immediately gets nerfed after he starts getting played (despite the fact that he was NOT over powered). Rengar performed just as well during worlds. Hell, even Pantheon did well when inSec was playing him. If Kha'Zix was supposedly OP during worlds, then so were Rengar and Pantheon.

comes out. He's pretty strong, but also buggy. Bugs get fixed, he starts doing well. He gets played by pros once, boom, that's the sound of the nerf cannon. Completely gutted to the lowest win rate.

In Korea was getting played as support. DFG gets removed and he gets gutted. None of those three things fit together. Why the fuck was he nerfed? As far as I can tell Riot saw him being played as support and thought "Woah, that guy is preventing LC$ Big plays with that stun, better gut him"

And yet has been overpowered as hell for months now and Riot has done almost nothing to nerf her. Favoritism at its finest.