I really think MOBA's isn't the best genre to develop story.
As much as I'm really excited for story development, I really wish Riot starts to move on to other types of games to create and develop story. A lot of people want an MMO which would be a massive project, there are other types of genre that can fit well for the league universe and would be a little bit smaller for a project, like a turn based strategy game (Fire Emblem) or real time strategy game (Warcraft 3).
However I do have to give props as you guys still develop plots and story even with such a genre that necessarily doesn't need it. Keep up the great work!!