Riot could learn a few things from Splatoon's ranked system
You know how in LoL, you could "potentially" be stuck in the same division forever? You could potentially win every game, but lose promos everytime, and despite having a positive winrate, you'd still be stuck. Loss and win streaks are also a huge factor, with a lot of "lucky" players being protected from being demoted and being stuck in the 5th division of a League, or simply dropping you from a few division when unlucky.
Splatoon 2 on the other hand has a much more forgiving ranked system, that also forces players to change division every few game.
In LoL, you have your league (Bronze, Silver, Gold, etc) and your division (V, IV, III, II, I). Within a same division, you have your LP, which rises and drops after every wins and loss. Upon reaching 100LP, you enter your promos, forcing you to win a best of three to reach a higher division, or a best of five for a higher League. After promotion, you reset at 0LP and are protected from demotion for a few games. After demotion, you retain some LP, which makes it easier to get into promotion, although players are still subject to losing their promos.
In Splatoon 2, you also have your league (C, B, A, etc.) and your division ( ex: A-, A, A+ ), but instead of having points that rise and drop after every match, you have a gauge that fills after every victory. Upon losing a match, you don't lose points, you maitain your progress toward your next promotion, instead, after losing a match, "cracks" appear over your gauge. After a few games, you will get either promoted or demoted depending on wheter you fill your gauge or if it gets shattered. IF you gauge shatters, you still retain a portion of your win progress, which might save you from demotion and preserve some progress toward the next rank. You also don't have to go through promotions best of 3/5 to climb.
In LoL terms, after every division, you would accumulate your wins and your loss:
Ex: You just got promoted to Silver 3, you now have 0 wins and 0 loss. You'll be promoted after 10 victories, or demoted after 8 loss, whichever comes first. You were able to outsmart your opponents, and out of your 15 following games, you lost 6, but won 10, congrats! You are now Silver 2. After the next 16 games, you won 8 but lost 8, your progress toward Silver 1 resets, but you are saved from demotion, and preserve 2 wins out of 10. You now decide to learn how to play with your feet, with little success, you lose 8 games out of 9, and get demoted. You are now back to Silver 3, but maintain 3 wins, allowing you to hopefully get back to Silver 2 faster.
What i really enjoy about Splatoon 2's ranked system is how forgiving it is, i know i will eventually get either promoted or demoted, but i don't have to go through the frustration of repetitively losing my promos, despite winning most of my games otherwise. I also don't feel like losing streaks are quite as punishing as they are in League. Losing 4 games in a row in LoL sets me back a lot, and i know i'll have to work really hard and play that many more games to get back all that i've lost. Every lost LP is LP that i'll have to grind back again, which can lead to very long grinds just to reach my promos, which i might lose.
In Splatoon 2, as long as i win more often than i lose, i WILL climb the ladder, it doesn't matter if i lose a few games, i still maintain my progress.
tl;dr: Splatoon 2's ranked system is much more forgiving, much less frustrating, and way steadier.