Some champions are simply too easy to play
etc. etc.
Look, I'm not saying these champs are overpowered or any of the sort. Let's say a new player choses someone like Riven, then he meets Garen top. Riven has a massive learning curve; Garen not so much. The Garen will win without a doubt. Not only do these champs turn games into free wins against beginners who choses more difficult champions, but these champions (at higher elos) will either completely lack counterplay or just be so predictable because of their lack of outplay potential and become useless.
I don't think anyone enjoys spending a lot of time mastering a new champ, then get roflstomped by some first time Katarina simply because the champ doesn't require any functioning braincells to do well with.

