Champion Mastery is a progression system added during season five that helps players to keep tck of experience with champions. Over the years, Champion Mastery hasn’t changed much and League of Legends players have an idea of how to update it.
Currently, Champion Mastery serves mainly as a Blue Essence sink since you need Champion Mastery Token and Blue Essence to upgde your Champion Mastery. Since the system received the last major change in season six with Mastery being earned in Howling Abyss, the players agree it’s fairly outdated and mundane to use in this day and age.