League of Legends ranked system consists of many hoops when trying to advance between divisions and even tiers in said divisions. Teamfight Tactics doesn't have any of that, which prompted players to voice their wish to boot the promos.
Riot Games may have an actual riot on their hands as players had an opportunity to compare two ranked systems on the same launcher for the first time.
League of Legends initially had the same ranked system as Teamfight Tactics does now - no barriers between divisions or division tiers. A few years down the line, Riot added the infamous promotional games.
For those not familiar with the game, players earn League Points (LP) on each victory and lose them if they are defeated. Once they accumulate 100 LP, players enter a best of three series where they need two wins from the three games in order to get promoted.
Failing promos results in series failure and loss of LP, meaning players will have to do at the very least three more matches if they want to get promoted.
Teamfight Tactics doesn't have promos. If a player happens to have 95 LP, the next victory will move them one tier up immediately. Losing the match will simply subtract the fitting number of League Points and if the loss is not a crushing one, players have the opportunity to advance the ladder in the match immediately after.
As you can imagine, the system without promotional series barriers is much less stressful and players in the matches are by extension less toxic since they don't feel as pressured to win the games.
Climbing the ladder would be more convenient because missing one LP doesn't mean you have to play another match just to qualify for promos, excess League Points carry over into the next tier and there is less anxiety overall.
No one from Riot responded to the thread by the time of writing but it's definitely caught some attention, standing at over 10,000 upvotes.