Doing it for the viewers is just as bad, if not worse.
League of Legends is meant to be a game you play, not simply watch. If they were doing it for Pros, then it would be based on at least some gameplay, but instead, they are doing it for Joe Shmoe watching a video online to entice him into trying to play the game. However, due to the game feel, people who try and play get turned away, along with existing people, causing a net negative.
The first and foremost thing a game designer needs to do when making and balancing a game is the gameplay and game feel, as that is the primary way the game's audience is supposed to interact with it. If a game is also fun to watch, that is a bonus on top, and good gameplay and game feel often lead into enjoyable content to watch.
If they want to make the game for viewers instead of the people actually playing the game, they should just stick to making movies.