Riot actually does show favortism. How long did trydamere and teemo go on for without a nerf? Then even when nerfed its slight. Also how many times has champions like Ryze been reworked. I use these three examples because they are the best. We have trydamere and Ryze, two champion owned by 2 of the bosses or is it former bosses of riot now. And teemo, the hamster that everyone has hated since his creation.
ryze has been reworked I believe more than any champion in the history of league.
Trydamere went what 3 seasons without a single change till a couple months ago with a 3 second nerf on his ult.
Teemo.... people have begged since I joined in season 4 for a nerf. As some champions simply have no way to outplay him and win lane against him. Trydamere for example. If you stack kit to kit, throw the towers in lane in the mix, trydamere will always loose even if the player is of lower skill. Why? Because all a teemo has todo is aa poke, save his q and w. Tryda can't sustain in lane and will be poked out of lane.
Another example of favortism
Riot hates shaco and doesnt want him in the LCS, note his recent nerf. Now im not using the nerf as proof of this, they actually stated this publically that they didnt want him to see time in the LCS on atleast 1 ocasion. Maybe more but I don't always follow the news.
Another, not acutal proof however the jungler 
Lcs pros, youtube challenger/master and diamond players have all said he's op in public videos no less. Not only that, but that he's been this way for way to long. Yet riot has done nothing about it. Yes it takes the person to actually know how he works but still he's one of the strongest choices in the jungle. Even stronger than shyvanna, per nerf.
That is why people don't stop saying riot favors champions. Because Riot openly and admitted and continues to prove it patch after patch. I'm not gonna say what needs buffed "cough" nunu's kits so weak i ban him if my team hoovers it "cough" or nerfed. But there are tons of pro's and players of all skill ranks constantly playing this game and when they all say the same thing and riot does nothing, it shows. Players don't like that. They want a fair game. Stick around long enough and you'll start to understand why players constantly complain about fair nerfs or buffs, or about champions that seem to never be nerfed,
you 
use to?
and the latest one: 
