Personally, I strongly oppose the Quest system

link for those wondering: http://nexus.leagueoflegends.com/2017/05/dev-on-missions/

So, Riot suggested adding a quest system to League. I oppose this because of a problem the article even MENTIONS. "This is a delicate area. It’s important to us that missions don’t negatively impact your games. This means missions can’t encourage players to play to lose or to play in sub-optimal ways" maybe you just haven't seen league like i have, but trust me , if u give a quest such as "get 3 wins as leona with an A grade or higher" u r going to have people who refuse to fight and risk dying, save damage for kills, not save team mates and risk dying etc.

Although a quest mechanic is cool in theory, i like league the way it is, and adding something that even slightly makes people play in a way that might lower my chances of winning a game is a very bad idea.