Ezreal 43.87% , receive only buff and his item are in a good spot
Lee Sin 36.63% Received buff last time and his item are in a good spot
Thresh 32.13% Only got adjustement toward his lantern and passive buff a long time ago, no change since and his item are good
Kai'Sa 29.41% Received nerf in the past but really minor and her item recently got buffed and Guinsoo didn't receive change so she is in a good spot
Vayne 27.86% Received multiple buff lately and her item got buffed and Guinsoo didn't got touched so she rised to a good spot also
Lucian 22.27 Receive good buff and ridiculous nerf to his W, most useless spell. Item got changed in his favor so he is in a good spot
Sivir 18.71% Crit item got reworked wich favored her in the meta so she is in a good spot
Sylas 18.27% New champion with extremely strong kit for nothing and received buff when he didn't deserve it, so it's a good spot I guess
Vladimir 17.32% Strong in general and scale really hard, no real nerf for a long time , good spot
Jarvan IV 16.55% Only receive buff so far and doesn't got real nerf , good spot
Yasuo 16.55% Got his last buff reverted but Conqueror got reworked in his favor and crit item also so good spot
Lissandra 14.15% Strong itemization and aftershock combination, strong in Pro play so strong spot
Riven 13.65% Her main runes got buffed for her playstyle and her item got buffed and Spear of Sojin got added, strong spot
Zed 13.46% Have a buff on the way, strong item overall and doesn't really fall off, strong spot
and the list goes to at least 10% play rate... 3/4 of the whole list on Op.gg are champion that received mostly buff and itemization change in their favor.
Meanwhile Quinn at 1.61% , reached max 5 % last year and got instantly nerfed because low popularity and ''oppressive''. I use my champion as reference but many champion could be used in said exemple. Riot is biased toward high play rate champion and they are either left untouched, buffed or receive ridiculous nerf that doesn't change the performance of the champion overall( Lucian W nerf is the best exemple I can say).
It need to stop. The bias toward high popularity champions make this game legit unfair for players that doesn't want to play FOTM and it sincerely sucks. People keep saying this game is dieing but actually , champions freedoms is dieing. You play the OP/pupular or you get bend down. It need to stop, NOW.