There is a system in place. The system is you. If you are having bad games and cannot carry teams, you are the only common denominator. The League system matches players with other players of similar skill - the enemy team is not challenger players and you don't have 4 allies that just started the game this week. Everyone gets heated sometimes, not just your team. For all you know, the enemy team may be raging harder than your own team in chat.
there are two different issues you listed and i need to know which one you're arguing about. The first issue is players becoming angry, toxic behavior. Threatening to AFK or feed.The second issue is team performance. they do relate to each other because team morale counts, but generally players become angry because they want to win, not because they want to lose. If you're angry because players can't stop typing during a game, mute them. If you're angry your team is underperforming, you must be the person to carry to victory
That being said, if you cannot seem to climb, regardless, the chances are that you are exactly where you belong in the elo poll. Are you saying you want to play against Challenger level players? There is a reason Diamond mains have multiple accounts in Diamond. And there is a reason Silver players cannot get out of Silver. Either you carry yourself to the elo where you belong, or you're already there.
One player makes up 20% of the team. That is a significant portion, and that is enough to have a outstanding impact on the game itself. Players who wreck through elo and climb fast are the one's who say very little, and carry very much. They do not get dragged down by 1 bad game out of 10 wins. But if you are not carrying the majority of the wins, and you are having trouble winning promo's, then there is a reason. And that reason is not your team, because the enemy team is at the same skill level as your own team
Are you saying Riot is teaming you with poor allies and strong enemies? No such system exists.