If we really want to get technical and look at how a lot of other games deal with ranking, they do have an ELO which correlates to your rank and league, but they also do have a hidden ELO which is actually the one being taken into consideration by the matchmaking. That hidden ELO is where the game is trying to evaluate your position and will swing a lot more than your league, since the league is supposed to be more stable. For instance, when you start an account, the game will attribute you an average hidden ELO, then match you with people of similar hidden ELO, and depending on your success or failure, will adjust the hidden ELO accordingly, and usually very dramatically until it can reduce the range to where your skill level is the most probably closest to. Once you have played enough games, you get delivered into the league that corresponds roughly to that. The hidden ELO however stays and if you get through a win streak, it will adjust immediately and increase the level of the adversaries you face, which can then be of the higher leagues compared to yours if you win enough. And if you keep winning, the rewards to your real ELO will be bigger and bigger to make you actually climb. On the other hand, loss streaks will dramatically lower your hidden ELO and suddenly match you with lower leagues past a point. Almost every multiplayer game works like this, where XIV doesn't.