A coach system? In a game that doesn't even have a sandbox mode, a robust replay system, customizable UI elements(or UI skins altogether), has had the same in-game announcer since forever, has no actual punishment/reward system other than some bull%%%% automated %%%% with a big margin error.
Did you know, Smite, a moba that released last freaking year, has a mastery system that rewards you with multiple unlockable skins you can pay with in-game currency(and not real money) and icons that are free? In fact, each character in the game has 3 skins you can unlock through mastery, 3 %%%%ing skins.
Did you know, League Of Legends, who became the benchmark of Moba's, has the biggest E-sports scene in the world(not reward-size), has existed for 5 years, has the largest playerbase to ever exist in PC-gaming and the largest number of online players to ever play a multiplayer game, rewards your mastery with just an emote and a number that goes from 1-7(5-7 soon to be implemented lol)?
But I digress, I think they are utterly incompetent to handle anything important that would benefit the game. Much less a coaching system that would benefit player experience. Only things one can do revolve around doing them by oneself: an educational youtube channel/blog/post or what have you. You could also advertise your coaching by creating chatrooms for people looking for coaching to join. Then joining games with them, connected with voicechat, to teach them the game.
Amazing music and art is all Riot's capable of producing at a respectable level, so yeah...